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HAProxy - Load balancer
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Willy Tarreau 4ef31cb5c2 BUG/MINOR: dns: always validate the source address in responses 
When we removed the use of connect() to reach DNS servers in 3.3 with
commit 2c7e05f80e ("MEDIUM: dns: don't call connect to dest socket for
AF_INET*"), we accidentally lost a check on the server's address in
responses, opening the possibility of spoofed DNS responses for someone
who knows both haproxy's IP:port and the transaction ID.

In practice, the impact is very low, because:
  - DNS servers IP addresses are almost always known, and often even among
    the widely used ones (1.1.1.1, 8.8.8.8 etc), and their port is 53.
  - all DNS "security" relies on the ignorance of the transaction ID and
    is possible source port, so if either the attacker is on-path and sees
    them, or it's off-path and has to guess them, but in any case it's
    trivial to spoof the known server in responses, with or without the
    check.

Regardless, let's not further weaken the protocol and do the check.

Thanks to Omkhar Arasaratnam for reporting this issue.

An interesting observation while testing this fix was that the code does
support UNIX dgram sockets (via connect()) but that since we don't bind
to a local UNIX socket to send requests, the server's recvfrom() doesn't
get any address and has nowhere to respond to. So in practice while the
code is designed to deal with UNIX sockets, these cannot work by design.

This fix must be backported to 3.2 where the commit above was backported.
2026-05-04 16:27:26 +02:00
.github CI: github: add DEBUG_STRICT=2 to ASAN jobs 2026-04-30 17:46:30 +02:00
addons DOC: otel: update the filter's status and URL in the docs 2026-05-04 14:38:35 +02:00
admin CLEANUP: fix typos and spelling in comments and documentation 2026-03-30 09:24:19 +02:00
dev CLEANUP: fix typos and spelling in comments and documentation 2026-03-30 09:24:19 +02:00
doc DOC: acme: document missing acme-vars and provider-name keywords 2026-05-04 14:44:53 +02:00
examples EXAMPLES: ssl: keylog entries are greater than 1024 2026-04-14 16:24:28 +02:00
include BUG/MINOR: quic: fix buffer overflow with sockaddr_in46 2026-05-04 10:49:49 +02:00
reg-tests BUG/MEDIUM: cli: fix master CLI connection slot leak on client disconnect 2026-04-30 17:06:19 +02:00
scripts BUG/MINOR: reg-tests: make shell syntax errors fatal 2026-04-22 15:18:22 +02:00
src BUG/MINOR: dns: always validate the source address in responses 2026-05-04 16:27:26 +02:00
tests TESTS: quic: add unit-tests for QUIC TX part 2025-09-08 14:49:03 +02:00
.cirrus.yml CI: cirrus-ci: bump FreeBSD image to 14-3 2025-10-09 14:06:48 +02:00
.gitattributes MINOR: Configure the cpp userdiff driver for *.[ch] in .gitattributes 2021-02-22 18:17:57 +01:00
.gitignore MINOR: tevt/dev: Add term_events tool 2025-01-31 10:41:50 +01:00
.mailmap DOC: update Tim's address in .mailmap 2021-09-16 09:14:14 +02:00
.travis.yml MEDIUM: mworker: remove USE_SYSTEMD requirement for -Ws 2024-11-20 12:07:38 +01:00
BRANCHES DOC: clarify the experimental status for certain features 2025-10-17 18:41:13 +02:00
BSDmakefile BUILD: makefile: commit the tiny FreeBSD makefile stub 2023-05-24 17:17:36 +02:00
CHANGELOG [RELEASE] Released version 3.4-dev10 2026-04-29 15:51:32 +02:00
CONTRIBUTING CLEANUP: assorted typo fixes in the code and comments 2025-04-02 11:12:20 +02:00
INSTALL MINOR: version: mention that it's development again 2025-11-26 16:11:47 +01:00
LICENSE LICENSE: add licence exception for OpenSSL 2012-09-07 13:52:26 +02:00
MAINTAINERS MAJOR: spoe: Let the SPOE back into the game 2024-05-22 09:04:38 +02:00
Makefile BUILD: otel: removed USE_OTEL, addon is now built via EXTRA_MAKE 2026-05-04 14:15:17 +02:00
README.md CI: github: add cross-zoo.yml in README.md 2026-04-20 11:47:20 +02:00
SUBVERS BUILD: use format tags in VERDATE and SUBVERS files 2013-12-10 11:22:49 +01:00
VERDATE [RELEASE] Released version 3.4-dev10 2026-04-29 15:51:32 +02:00
VERSION [RELEASE] Released version 3.4-dev10 2026-04-29 15:51:32 +02:00

README.md

HAProxy

AWS-LC Illumos NetBSD CrossCompile FreeBSD VTest

HAProxy logo

HAProxy is a free, very fast and reliable reverse-proxy offering high availability, load balancing, and proxying for TCP and HTTP-based applications.

Installation

The INSTALL file describes how to build HAProxy. A list of packages is also available on the wiki.

Getting help

The discourse and the mailing-list are available for questions or configuration assistance. You can also use the slack or IRC channel. Please don't use the issue tracker for these.

The issue tracker is only for bug reports or feature requests.

Documentation

The HAProxy documentation has been split into a number of different files for ease of use. It is available in text format as well as HTML. The wiki is also meant to replace the old architecture guide.

Please refer to the following files depending on what you're looking for:

  • INSTALL for instructions on how to build and install HAProxy
  • BRANCHES to understand the project's life cycle and what version to use
  • LICENSE for the project's license
  • CONTRIBUTING for the process to follow to submit contributions

The more detailed documentation is located into the doc/ directory:

License

HAProxy is licensed under GPL 2 or any later version, the headers under LGPL 2.1. See the LICENSE file for a more detailed explanation.