Red Hat Bugzilla – Bug 451615
CVE-2008-2364 httpd: mod_proxy_http DoS via excessive interim responses from the origin server
Last modified: 2014-11-30 23:17:40 EST
Common Vulnerabilities and Exposures assigned an identifier CVE-2008-2364 to the following vulnerability:
The ap_proxy_http_process_response function in mod_proxy_http.c in the
mod_proxy module in the Apache HTTP Server 2.0.63 and 2.2.8 does not limit the
number of forwarded interim responses, which allows remote HTTP servers to
cause a denial of service (memory consumption) via a large number of interim
Fixed upstream in: 2.2.9
Upsteam patch in 2.2.x branch:
There are two separate issues here:
1) a stack exhaustion and CPU consumption issue. This affects all upstream
httpd 2.0.x releases from through to 2.0.63, and 2.2.0 through to 2.2.8.
Whilst reading interim responses, CPU consumption is O(N^2) with number of
responses read, and for each response the stack space required is O(N) likewise.
This presents a denial of service attack either by CPU consumption or by the
eventual process crash due to stack limit being reached.
2) a heap exhaustion issue. This affects upstream httpd releases 2.2.7 and
2.2.8 only. This presents a denial of service by heap exhaustion.
Red Hat Enterprise Linux 2 is not affected by either of these issues.
Red Hat Enterprise Linux 3, 4, and 5 are affected by issue (1) only.
Fedora 8 and 9 are affected by both (1) and (2) as of the most recent 2.2.8 updates.
Note that both these issues only affect a forward proxy configuration; where a
user can be coerced into accessing a malicious origin server through the proxy,
that server attack the proxy as described above.
We do not plan to issue an asynchronous RHSA at the moment because of this
issue, due to a limited impact. This issue can cause high CPU consumption, or
stack overflow (exhaustion of stack memory, not stack-based buffer overflow)
causing a crash of httpd child process. With default MPM - worker MPM - such
crash can only impact requests of one particular user.
Additionally, as the issue can only be triggered by a malicious web server to
which requests are proxied, impact on the typical use of mod_proxy module is
quite minimal. mod_proxy is usually used in reverse proxy setups, where
requests are proxied to trusted (internal) web servers. Forward proxy setups,
where requests can be proxied to arbitrary web server, are not very common, due
to a lack of caching support. Squid web proxy is more commonly used in such cases.
We plan to fix this issue in some future httpd update once there is some
higher-severity issue to be fixed.
httpd-2.2.9-1.fc9 has been pushed to the Fedora 9 stable repository. If problems still persist, please make note of it in this bug report.
httpd-2.2.9-1.fc8 has been pushed to the Fedora 8 stable repository. If problems still persist, please make note of it in this bug report.
Release note added. If any revisions are required, please set the
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A flaw was found in the mod_proxy module. An attacker who has control of a web server to which requests are being proxied could cause a limited denial of service due to CPU consumption and stack exhaustion. (CVE-2008-2364)
This issue has been addressed in following products:
Red Hat Certificate System 7.3
Via RHSA-2010:0602 https://rhn.redhat.com/errata/RHSA-2010-0602.html
This issue has been addressed in Red Hat Enterprise Linux 3, 4 and 5. For more information see: