[v2.7] CVE-2013-2175 : haproxy may crash when using header occurrences relative to the tail
David Torgerson reported an haproxy crash with enough traces to
diagnose
the cause as being related to the use of a negative occurrence number
in
a header extraction, which is used to extract an entry starting from
the
last occurrence.
—- summary —-
Configurations at risk are those which make use of “hdr_ip(name,–1)”
(in
1.4) or any hdr_* variant with a negative occurrence count in 1.5,
or
the “usesrc hdr_ip(name)” statement in both 1.4 and 1.5. These
configurations may be crashed when run with haproxy 1.4.4 to 1.4.23 or
development versions up to and including 1.5-dev18. Versions 1.4.24
and
1.5-dev19 are safe.
—- quick workaround —-
A workaround consists in rejecting dangerous requests early using
hdr_cnt(), which is available both in 1.4 and 1.5 :
block if { hdr_cnt() ge 10 }
—- details —-
When a config makes use of hdr_ip(x-forwarded-for,–1) or any such
thing
involving a negative occurrence count, the header is still parsed in
the
order it appears, and an array of up to MAX_HDR_HISTORY entries is
created.
When more entries are used, the entries simply wrap and continue this
way.
A problem happens when the incoming header field count exactly divides
MAX_HDR_HISTORY, because the computation removes the number of
requested
occurrences from the count, but does not care about the risk of
wrapping
with a negative number. Thus we can dereference the array with a
negative
number and randomly crash the process.
The bug is located in http_get_hdr() in haproxy 1.5, and
get_ip_from_hdr2()
in haproxy 1.4. It affects configurations making use of one of the
following
functions with a negative occurence number :
- hdr_ip(, ) (in 1.4)
- hdr_*(, ) (in 1.5)
It also affects “source” statements involving “hdr_ip()” since
that
statement implicitly uses –1 for :
- source 0.0.0.0 usesrc hdr_ip()
This bug has been present since the introduction of the negative
offset
count in 1.4.4 via commit bce70882.
CVE-2013-2175 was assigned to this bug.
Special thanks to David Torgerson who provided a significant number of
traces, and to Ryan O’Hara from Red Hat for providing a CVE id.
—- links —-
1.4-stable patch for version <= 1.4.23 :
http://git.1wt.eu/web?p=haproxy-1.4.git;a=commitdiff;h=f534af74ed
1.4.24 source code:
http://haproxy.1wt.eu/download/1.4/src/haproxy-1.4.24.tar.gz
1.5-dev patch for versions <= 1.5-dev18 :
http://git.1wt.eu/web?p=haproxy.git;a=commitdiff;h=67dad2715b
1.5-dev19 source code:
http://haproxy.1wt.eu/download/1.5/src/devel/haproxy-1.5-dev19.tar.gz
(from redmine: issue id 2114, created on 2013-06-21, closed on 2013-07-03)
- Relations:
- parent #2098 (closed)
- Changesets:
- Revision d2207b3c by Natanael Copa on 2013-06-21T13:37:42Z:
main/haproxy: security upgrade to 1.4.24 (CVE-2013-2175)
fixes #2114