Upstream-Status: Backport CVE: CVE-2022-22707 Signed-off-by: Ross Burton From 27103f3f8b1a2857aa45b889e775435f7daf141f Mon Sep 17 00:00:00 2001 From: povcfe Date: Wed, 5 Jan 2022 11:11:09 +0000 Subject: [PATCH] [mod_extforward] fix out-of-bounds (OOB) write (fixes #3134) (thx povcfe) (edited: gstrauss) There is a potential remote denial of service in lighttpd mod_extforward under specific, non-default and uncommon 32-bit lighttpd mod_extforward configurations. Under specific, non-default and uncommon lighttpd mod_extforward configurations, a remote attacker can trigger a 4-byte out-of-bounds write of value '-1' to the stack. This is not believed to be exploitable in any way beyond triggering a crash of the lighttpd server on systems where the lighttpd server has been built 32-bit and with compiler flags which enable a stack canary -- gcc/clang -fstack-protector-strong or -fstack-protector-all, but bug not visible with only -fstack-protector. With standard lighttpd builds using -O2 optimization on 64-bit x86_64, this bug has not been observed to cause adverse behavior, even with gcc/clang -fstack-protector-strong. For the bug to be reachable, the user must be using a non-default lighttpd configuration which enables mod_extforward and configures mod_extforward to accept and parse the "Forwarded" header from a trusted proxy. At this time, support for RFC7239 Forwarded is not common in CDN providers or popular web server reverse proxies. It bears repeating that for the user to desire to configure lighttpd mod_extforward to accept "Forwarded", the user must also be using a trusted proxy (in front of lighttpd) which understands and actively modifies the "Forwarded" header sent to lighttpd. lighttpd natively supports RFC7239 "Forwarded" hiawatha natively supports RFC7239 "Forwarded" nginx can be manually configured to add a "Forwarded" header https://www.nginx.com/resources/wiki/start/topics/examples/forwarded/ A 64-bit build of lighttpd on x86_64 (not known to be affected by bug) in front of another 32-bit lighttpd will detect and reject a malicious "Forwarded" request header, thereby thwarting an attempt to trigger this bug in an upstream 32-bit lighttpd. The following servers currently do not natively support RFC7239 Forwarded: nginx apache2 caddy node.js haproxy squid varnish-cache litespeed Given the general dearth of support for RFC7239 Forwarded in popular CDNs and web server reverse proxies, and given the prerequisites in lighttpd mod_extforward needed to reach this bug, the number of lighttpd servers vulnerable to this bug is estimated to be vanishingly small. Large systems using reverse proxies are likely running 64-bit lighttpd, which is not known to be adversely affected by this bug. In the future, it is desirable for more servers to implement RFC7239 Forwarded. lighttpd developers would like to thank povcfe for reporting this bug so that it can be fixed before more CDNs and web servers implement RFC7239 Forwarded. x-ref: "mod_extforward plugin has out-of-bounds (OOB) write of 4-byte -1" https://redmine.lighttpd.net/issues/3134 (not yet written or published) CVE-2022-22707 --- src/mod_extforward.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/src/mod_extforward.c b/src/mod_extforward.c index ba957e04..fdaef7f6 100644 --- a/src/mod_extforward.c +++ b/src/mod_extforward.c @@ -715,7 +715,7 @@ static handler_t mod_extforward_Forwarded (request_st * const r, plugin_data * c while (s[i] == ' ' || s[i] == '\t') ++i; if (s[i] == ';') { ++i; continue; } if (s[i] == ',') { - if (j >= (int)(sizeof(offsets)/sizeof(int))) break; + if (j >= (int)(sizeof(offsets)/sizeof(int))-1) break; offsets[++j] = -1; /*("offset" separating params from next proxy)*/ ++i; continue; -- 2.25.1