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MaraDNS’ security

For people with a security bug to report: post it here. Please be aware that any abuse of this feature may result in being blocked.

Here are all of the supported versions of MaraDNS without any known security issues:

For users of older versions of MaraDNS or Deadwood: Please update your package; there is an update guide available.

For people who just want to quickly get current with MaraDNS’ security history should jump to the history section. Note that MaraDNS’ last known security problem was fixed on or before October 24, 2022.

I also have a comparison of DNS servers’ security history.

Note that neither MaraDNS nor Deadwood have DNSSEC support.

MaraDNS should be a secure DNS server.

The reason why I say should be instead of "is" is because I find claims of security very pretentious. There is no way that I can guarantee that a piece of code as complex as a recursive DNS server is completely free from security bugs.

What I can guarantee, however, is that such bugs are very unlikely in MaraDNS, since the design has security checks and balances which minimize the chance of there being a security hazard in the code.

Why code is insecure

The main reason why code is insecure is because the code in question has undefined results when fed data which is in a different form than what the author of the code expected. The simplest case of this is the buffer overflow, where a program is fed a string far longer than the program was designed to handle.

Another example is the "cache poison" bug which ancient versions of another DNS implementation had. With this bug, it was a trivial matter to tell the DNS server that, for example, had an ip address of say,, which really points to some sleazy site that installs spyware. Why did this bug exist? Because the original authors of this server did not expect remote servers to deliberately give out incorrect IP addresses.

How MaraDNS avoids these problems

First of all, MaraDNS uses a special string library which is resistant to buffer overflows. It does this by having a maximum allowed size for a string--any attempt to make a string larger than the maximum allowed size causes the string library to return an error instead of overflowing a buffer. In addition, the string library allocates an extra three bytes for each string object, as a cushion against possible boundary conditions (there was one case with another program which strived to be secure where a one-byte buffer overflow resulted in a remote root exploit).

Second of all, MaraDNS protects herself from cache poisoning without ever discarding glue records is by handling out-of-bailiwick records differently, depending on where the offending records are. The actual rules are fairly complex, and detailed in a document called " ".

Third of all, I have extensively read Dan Bernstein's notes on DNS implementation before implementing MaraDNS. Two ideas for implementing DNS security discussed on Dan's pages have been implemented in MaraDNS:

  • When the recursive nameserver is performing queries, MaraDNS uses a securely generated pseudo-random-number-generator to generate the query ID, and the lower 12 bits of the query source port. This means that a given attempt to spoof a reply to MaraDNS has less than a 1 in 250 million chance of succeeding.
  • MaraDNS uses a FIFO queue to delete unused records when the cache starts to fill up. The algorithm is simple: Every time a record is accessed, it is placed at the top of the list. When memory fills up, MaraDNS deletes records at the bottom of the list. This allows MaraDNS to act in a very graceful manner when the cache starts to fill up.
Some known security problems are avoided: MaraDNS does not use printf() in a manner which would make format string vulnerabilities possible; MaraDNS does not use any of the potentially dangerous globing functions; and MaraDNS signal handlers are very short, avoiding the problems caused by poor signal handler construction.

I go though the code, and when I find anything which has the possibility of allowing the data to be in an undefined state, I revise the code in question. For example, when I was looking through the code in the 0.8.35 release of MaraDNS; I found a case where the data could potentially become undefined. In more detail, if certain strings could not be allocated or copied over--cases which can never happen--the code which removes elements from the cache would attempt to free() unallocated memory later on. Even though this was a case where it was impossible to exploit the code in question, I felt it was prudent to update the code to not have this problem--hence the vaguely worded "security update" for the 0.8.99 release of MaraDNS.

MaraDNS uses a minimum number of external libraries. This minimizes the impact of insecure code not under MaraDNS' direct control causing security problems with MaraDNS. This stops MaraDNS from having the kind of remote full-control exploit BIND9 had when it linked to an insecure version of the OpenSSL library.

MaraDNS also mandates that the server is run as an unprivileged user, and strongly encourages MaraDNS to be run in a chroot() environment. In addition, the DNS cache uses a separate data structure than the local DNS records, making it difficult, if not impossible, for the cache at affect the local records. This design means that, even if there is a security hole in MaraDNS, the possibility of such a security hole allowing the attacker having elevated privileges is next to zero.

The security history of MaraDNS

MaraDNS has never had a security problem worse than remote denial of service.

There have been 23 security problems found; none are worse than denial of service (To be fair, three corrupt memory but in a way where the corrupted memory is not controlled by an attacker). One was a security problem caused by broken behavior in Linux's kernel that affected stable versions of MaraDNS. There are also theoretical (less than minor) security problems caused by some research in to AES' implementation on modern cached processors which have been addressed.

Here are all of the security problems ever discovered with MaraDNS:

  1. The first major security problem was discovered by Roy Arends, one of the BIND developers, and was caused by the fact that very early versions of MaraDNS did not check to see whether a given DNS packet was a question or an answer. This was fixed well before the 1.0 release of MaraDNS.

    Since a DNS answer looks like a DNS question, with the exception of a one-bit difference, this bug allowed an attacker to send a spoofed DNS packet which would result in MaraDNS sending an answer to herself (or to another MaraDNS server), which would result in another answer being sent, and so on.

    The reason this security glitch passed through was because of an overzealous effort to honor the RFC spirit to be "liberal in what one accepts and conservative in what one sends". Since then, I have gone over the DNS spec to see if their are any other cases where a malformed packet could cause this kind of security problem, and have made an effort that any such cases in MaraDNS no longer exist.

    CVE number: CVE-2004-0789
    Impact: Remote denial of service.

  2. Another major security problem was found by myself when performing an audit of the code during the beta test cycle. It involved the decompression code, and was caused because DNS compression is difficult to implement, and easy to create security holes with. I resolved this issue by completely rewriting the code in question with security in mind. This security problem was fixed in MaraDNS 0.9.01 (the rewrite came later).

    CVE number: CVE-2002-2097
    Impact: Remote denial of service.

  3. Another major problem, which allowed a remote denial of service, was caused by some broken behavior in the Linux kernel. People using BSD or other kernels were not affected by this security problem. This security problem was fixed in MaraDNS 1.0.28 and in MaraDNS 1.1.35.

    CVE number: None
    Impact: Remote denial of service.

  4. One old minor security problem involved the seed for the pseudo-random number generator. In cases where there was an ASCII null in the key for the pseudo-random number generator, MaraDNS would have less than a full 128 bits of entropy for the seed. There was also a related issue, even more minor, where, in certain rare circumstances, multiple instances of MaraDNS could potentially generate the same pseudo-random numbers, if two copies of MaraDNS used the same static random seed file, and were started at the same time. These issues were fixed before the release of MaraDNS 0.8.24.

    CVE number: None
    Impact: Theoretical spoofing of DNS records.

  5. Another minor problem, more recently discovered, was only present in the development (1.1) branch of MaraDNS. The fetchzone tool did not perform enough input validation and was vulnerable to specially formed packets that could send out-of-bailiwick data. I fixed this problem both ways; first by giving the fetchzone tool more input validation. Later on, I modified the csv2 parser to not accept the kind of data which would have triggered the fetchzone security bug. This issue was fixed in MaraDNS 1.1.38 (the csv2 improvements appeared in MaraDNS 1.1.47).

    CVE number: None
    Impact: Spoofing of DNS records.

  6. A theoretical security problem with the underlying random number generator that MaraDNS uses to generate secure random numbers was discovered by D. J. Bernstein. Since the underlying random number generator uses a fairly simple key schedule (well, a simple key schedule for a cryptographic routine), and since the random number generator uses table lookups, modern CPUs will very slightly vary (on the order of billionths of a second) in the amount of time used to generate a secure random number, depending on the underlying key. Bernstein needed to examine over 200 million packets, obtaining very precise timing information on each packet, to extract a key.

    I worked around this security problem by having the random number generator rekey every million packets. These changes were done in MaraDNS 1.0.27 and 1.1.35.

    Mailing list posting describing this issue

    CVE number: None
    Impact: Theoretical remote spoofing of DNS records.

  7. More recently, Dag Arne Osvik, Adi Shamir (the "S" in RSA), and Eran Tromer discovered some sophisticated cache data leakage attacks against AES, the algorithm from which MaraDNS' secure random number generator is derived. I have responded to this issue by tweaking MaraDNS' secure random number generator to essentially not leak sensitive key data via cache lookups. These changes were done for MaraDNS 1.0.35 and 1.1.56.

    Patch which describes the issue and how I work around it

    CVE number: None
    Impact: Theoretical local spoofing of DNS records.

  8. There was a remote denial of service problem where someone could disable MaraDNS' recursion by sending thousands of specially crafted DNS packets per second to a server running MaraDNS. MaraDNS would function normally again once the DNS packets were no longer being sent. This affected all versions of MaraDNS, and was fixed in MaraDNS, 1.0.40, and 1.3.04.

    CVE number: None
    Impact: Remote Denial of Service.

  9. MaraDNS would leak approximately 20 bytes whenever an invalid DNS packet was received. This leak would have allowed an attacker to cause MaraDNS to allocate an arbitrary large amount of memory by sending a very large number of invalid DNS packers to the server running MaraDNS. This affected the 1.2 and 1.3 branches of MaraDNS, and was fixed in MaraDNS and the 1.3.04 release of MaraDNS.

    CVE number: CVE-2007-3114
    Impact: Remote denial of service.

  10. MaraDNS would leak about 300 bytes whenever a specially crafted DNS packet (either one with a non-0 Opcode, or a non-1 Class) was sent to the server. This leak would have allowed an attacker to cause MaraDNS to allocate an arbitrary large amount of memory by sending a very large number of invalid DNS packers to the server running MaraDNS. This affected the 1.2 and 1.3 branches of MaraDNS, and was fixed in MaraDNS and the 1.3.05 releases of MaraDNS.

    CVE number: CVE-2007-3115 and CVE-2007-3116
    Impact: Remote denial of service.

  11. A CNAME record in MaraDNS' authoritative database could be corrupted by someone sending a specially crafted DNS packet. This affected the 1.0, 1.2, and 1.3 branches of MaraDNS, and was fixed in MaraDNS 1.0.41,, and

    CVE number: CVE-2008-0061
    Impact: Remote denial of service.

  12. A bug introduced in MaraDNS 1.3.03 (January 2007): Hostnames that incorrectly not end with a dot result in a string being deallocated then used.

    MaraDNS 1.2 does not have this issue.

    This issue can not be exploited from zones loaded using DNS's zone transfer mechanism; fetchzone filters data obtained this way. This issue can only be exploited in the unusual case of an attacker having control of the contents of a csv2 zone file to be parsed by MaraDNS.

    This issue, on Linux systems, results in a null pointer dereference that terminates that MaraDNS process.

    This issue was fixed in MaraDNS 1.4.03 and, released February 2, 2010.

    CVE number: CVE-2010-2444
    Impact: Denial of service.

  13. An array of integers was allocated in bytes instead of sizeof(int) units. The resulted in a buffer being too small, allowing it to be overwritten. Since the data placed in the overwritten array can not be remotely controlled (it is a list of increasing integers), there is no way to increase privileges exploiting this bug.

    This bug was fixed in MaraDNS, MaraDNS 1.4.06, and MaraDNS 2.0.02, released on or before February 5, 2011. This bug also impacts MaraDNS 1.0 and MaraDNS 1.2; since these versions of MaraDNS have passed their end of life, they have not been updated.

    More information is at this blog entry.

    CVE number: CVE-2011-0520
    Impact: Denial of service.

  14. MaraDNS 1's recursive resolver did not use a randomized hash, making it vulnerable to certain denial of service attacks. This bug was fixed in MaraDNS and MaraDNS 1.4.10.

    More information is at this blog entry (, this blog entry (, as well as this blog entry (

    CVE numbers: CVE-2011-5055 and CVE-2012-0024
    Impact: Denial of service.

  15. MaraDNS 2's authoritative server did not use a randomized hash, so could be subject to certain denial of service attacks in the rare and unusual case of an attacker being able to control its zone files. This bug was fixed in MaraDNS 2.0.05, released February 12, 2012.

    CVE number: CVE-2011-5056
    Impact: Denial of service from a trusted user

  16. Deadwood releases before Deadwood 3.2.02 allow entries to remain in the cache for a long time. In light of the Ghost domain exploit (PDF file), this is a security problem.

    Deadwood 3.2.02 is updated to only allow entries to remain in the cache for one day. If max_ttl is set, one can choose to store entries in the cache for up to 90 days.

    MaraDNS 1.4.11 and MaraDNS 2.0.06 include this updated version of Deadwood. These releases were done on or before March 11, 2012.

    CVE number: CVE-2012-1570
    Impact: Canceled names can still be cached by Deadwood. For example, if points to a phishing page, and the domain is pulled by ICANN, Deadwood might have kept in its cache long after the domain was removed upstream.

  17. MaraDNS 1 releases before 1.4.12 and allow entries to remain in the cache for a long time. In light of the Ghost domain exploit (PDF file), this is a security problem.

    This bug does not affect users of MaraDNS 2, but Deadwood has a similar fix (see above).

    This update was done on March 17, 2012.

    CVE number: CVE-2012-1570
    Impact: Canceled names can still be cached by MaraDNS 1. For example, if points to a phishing page, and the domain is pulled by ICANN, MaraDNS 1 might have kept in its cache long after the domain was removed upstream.

  18. While looking over the source code to Deadwood, I discovered that Deadwood 3 releases before Deadwood-3.2.03d have a security issue caused by a programming error I made.

    Under certain exceptional circumstances, it may have been possible to perform a blind spoofing attack against unpatched releases of Deadwood. The IP performing the blind spoofing attack needs to appear to have permission to perform full recursion with Deadwood in order to carry out the attack.

    Upgrading will fix the bug. Then again, administrators who already perform good practices, making sure that only authorized IPs can use Deadwood recursively (pretty much mandatory in light of DNS amplification attacks) will only be affected by this bug if either a machine with an authorized IP is compromised, or if it is possible for the attacker to send the Deadwood server a packet with a spoofed IP.

    This update was done before December 2, 2013. MaraDNS 2.0.07d, Deadwood 3.2.03d, and MaraDNS 1.4.13 (as well as any future releases) are patched against this bug. Deadwood 2.3.08 is not affected by this bug.

    CVE number: None
    Impact: Possible blind spoofing of records

  19. There has been a long-standing bug in Deadwood (ever since 2007) where bounds checking for strings was not correctly done under some circumstances.

    Because of this, it has been possible to send Deadwood a “packet of death” which will crash Deadwood. Since the attack causes out-of-bounds memory to be read, but not written to, the impact of the bug is denial of service. It appears this attack can only be exploited by an IP with permission to perform recursive queries against Deadwood.

    This bug is fixed in Deadwood 3.2.05 and Deadwood 2.3.09. MaraDNS 2.0.09 and 1.4.14 have been updated to include Deadwood 3.2.05. The fix was made on February 12, 2014.

    Note that this bug only affects users of the Deadwood recursive resolver.

    CVE number: CVE-2014-2031 and CVE-2014-2032
    Impact: Remote denial of service

  20. Deadwood (MaraDNS 2.0) might be vulnerable to CERT VU#264212. That in mind, I have made MaraDNS releases (MaraDNS 2.0.11, Deadwood 3.2.07, and MaraDNS 1.4.16) with some code added to harden Deadwood and MaraDNS against CERT VU#264212. The fix was made before January 30, 2015.

    CVE number: CERT VU#264212
    Impact: Possible remote denial of service

  21. In the zoneserver daemon, free() was being called against a memory location whose value was uninitialized (and therefore random).

    This bug allows a denial of service attack; by making the zoneserver daemon free an invalid memory location, it was possible to terminate the zoneserver process. I do not know whether or not this bug is remotely exploitable.

    I now always initialize the memory location in question. The MaraDNS 2.0.12 release, made on August 19, 2015, fixes this bug.

    CVE number: None
    Impact: Possible remote denial of service

  22. There are two buffer overflows (actually, one buffer overflow and one buffer underflow) in ParseMaraRc.c. One of the buffer overruns can not be exploited, the other is a difficult to exploit buffer overflow (actually, underflow) in the mararc parser. The workaround is to not let random people edit the mararc file (which is usually in /etc and owned by root); the fix is in MaraDNS 2.0.13, release September 25, 2015.

    I checked, and, yes, MaraDNS 1.0.00 from 2002 had this particular bug. Most of the things like this come from the 2001-2002 codebase; I wrote too much code too quickly because there was a hurry to have an open-source DNS server that wasn’t BIND at the time.

    The exploit is very limited. It’s not possible to write to any memory with this bug; it only allows MaraDNS to read from a memory location she should not read from.

    CVE number: None
    Impact: It might be possible to make MaraDNS not start if one controls the mararc file MaraDNS reads at start-up time. Then again, anyone who controls that file could just more simply add a syntax error.

  23. There is a buffer overflow (actually, underflow) which allows an out of bounds memory location to be overwritten with the output of malloc() in Deadwood.

    It is unknown whether this buffer underflow is remotely exploitable; it has only been seen on systems where there is no default gateway route.

    This issue was fixed in Deadwood 3.2.09 and MaraDNS 2.0.13 on September 25, 2015.

    CVE number: None
    Impact: Possibly a remote denial of service.

  24. There was a theoretical issue with the cryptographic code in Deadwood, where a standards-compliant compiler might not generate correct secure random numbers (used for the query ID and query source port). I can not find a compiler which actually generates insecure code (I tested against gcc 3.2.3, gcc 4.8.5, gcc 7.3.0, clang 3.4.2, and clang 5.0.1), but in the interest of caution, I am making a security update, and have added tests to make sure this bug does not manifest itself when run against multiple compilers and compile flags (it’s only an issue with -O2 and -O3 in clang using a different implementation of RadioGatún[32]).

    This issue was fixed in Deadwood 3.2.12, released on August 15, 2018.

  25. The new Lua-based DNS servers, coLunacyDNS and mmLunacyDNS had issues where the string hash compression code was insecure, which could result in remote denial of service attacks under some conditions. This was an issue in the Lua code being used, which was fixed by patching Lunacy, the MaraDNS-specific fork of Lua.

    These issues did not affect MaraDNS nor Deadwood.

    This issue was fixed in MaraDNS 3.5.0012, released on August 12, 2020.

  26. The LUA-based coLunacyDNS server before 1.0.010 had a bug where, if it was not bound to an IPv6 address, it would call FD_ISSET on a connection not set up for the select() list. Since Ubuntu 20.04’s toolchain considers this a “buffer overflow”, I am marking this bug as a security issue of unknown impact.

    Neither the “MaraDNS” nor “Deadwood” services are impacted by this problem. The workaround is to bind coLunacyDNS to an IPv6 address; the fix is in commit 964d7892 which is part of coLunacyDNS 1.0.010 (MaraDNS 3.5.0018).

    This issue was found and fixed in December of 2020.

  27. The version of coLunacyDNS included with MaraDNS between versions 3.5.0008 (actually 3.5.0008 had mmLunacyDNS with the same issue and coLunacyDNS was added in 3.5.0009) and 3.5.0020 was not patched against CVE-2014-5461.

    Note that:

    • I am not able to actually exploit this issue with the version of Luancy (Lua) coLunacyDNS uses
    • This issue only affects the relatively new coLunacyDNS server (and may not affect it); it does not affect MaraDNS and it does not affect Deadwood
    • This would only be an issue on systems where an attacker can somehow affect the configuration file coLunacyDNS uses
    • The impact surface for this issue is, at worst, very very small

    This issue was fixed in coLunacyDNS 1.0.011 included with the MaraDNS 3.5.0021 release made on July 28, 2021.

    CVE number: CVE-2014-5461
    Impact: Possible local buffer overflow

  28. Xiang Li from Network and Information Security Lab, Tsinghua University discovered a way where “Ghost domains” could stay in the cache longer than max_ttl allows. I have integrated some measures to minimize the impact of these issues so that caching can not be abused to keep a rogue domain, already deleted upstream, cached for an inordinate amount of time.

    The attacks require an attacker who can perform queries against a recursive instance of Deadwood. The only impact is that entries may be cached longer than desired.

    This issue was fixed in Deadwood 3.5.0022 released on May 7, 2022, and in Deadwood 3.4.03 released on August 3, 2022. To allow other DNS server developers ample time to fix and patch the issue, I kept a 90-day embargo. I made the issue public on August 1, 2022, after working with other DNS implementors and getting the green light from them first.

    CVE number: CVE-2022-30256
    Impact: Records can be kept cached longer than desired

  29. Xiang Li from Network and Information Security Lab, Tsinghua University discovered a minor security bug where sometimes Deadwood would perform more than 83 queries to solve a given request.

    The attacks require an attacker who can perform queries against a recursive instance of Deadwood and to control replies from a server Deadwood queries. This only affects setups where root_servers is set in the Deadwood dwood3rc configuration file.

    This issue was fixed in Deadwood 3.5.0024 released on October 24, 2022, and in Deadwood 3.4.06, also released on October 24, 2022.

    CVE number: None
    Impact: Deadwood would make more than 83 queries to solve a single request

  30. MaraDNS releases before MaraDNS 3.5.0030 and 3.4.09 did not fully support RFC8482. This allowed ANY queries to be used to facilitate distributed denial of service attacks. While the impact is low with MaraDNS, since it does not have large DNS packet support, MaraDNS has been updated to fully support RFC8482.

    This update was made on or before November 26, 2022. The 2022-11-25 release of Deadwood.exe and the 2022-11-26 release of maradns.exe are patched against this issue.

    CVE number: None
    Impact: It was easier to use MaraDNS to facilitate some kinds of denial of service attacks.

  31. The authoritative server in MaraDNS releases before MaraDNS 3.5.0026 and MaraDNS 3.4.10 had an issue where it is possible to remotely terminate the MaraDNS process with a “packet of death”. The Deadwood recursive resolver was not affected by this bug, nor was coLunacyDNS.

    This bug was fixed on May 2, 2023.

    CVE number: CVE-2023-31137
    Impact: Remote denial of service