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CVE-request: apache's mod-fcgid does not respect configured FcgidMaxProcessesPerClass in VirtualHost
From: Daniel Kahn Gillmor <dkg () fifthhorseman net>
Date: Thu, 15 Mar 2012 14:39:40 -0400

Version 2.3.6 of mod-fcgid (the current published version from ASF according to [0]) has a known problem that FcgidMaxProcessesPerClass directives are not honored when they appear inside a VirtualHost stanza.

This is presents a risk for a denial of service because it means that a remote attacker can violate the intent of the admin and overwhelm the server running fcgid.

Could a CVE be assigned for this vulnerability?

If the admin declares that a given virtualhost should be limited to X fastcgi processes (often in order to constrain RAM usage by the vhost), any remote user can issue X+1 (or 10X, or whatever) concurrent GET requests, which defeats the documented limit, and can result in heavy swap or the oom-killer, which can cause a DoS on other services on the host.

This bug has been fixed since the release of 2.3.6 in upstream's svn (r1037727 of https://svn.apache.org/repos/asf/httpd/mod_fcgid/trunk) with a narrowly-targeted one-line patch:

--- modules/fcgid/fcgid_spawn_ctl.c     (revision 1037726)
+++ modules/fcgid/fcgid_spawn_ctl.c     (revision 1037727)
@@ -178,7 +178,7 @@
         if (current_node->inode == command->inode
             && current_node->deviceid == command->deviceid
             && !strcmp(current_node->cmdline, command->cmdline)
-            && current_node->vhost_id == sconf->vhost_id
+            && current_node->vhost_id == command->vhost_id
             && current_node->uid == command->uid
             && current_node->gid == command->gid)
             break;

But this patch hasn't made it to any released version.

Debian has plans to release a Debian Security Advisory for the issue and will resolve it with the above patch.

This problem is also documented at:

 https://issues.apache.org/bugzilla/show_bug.cgi?id=49902
 http://bugs.debian.org/615814

Regards,

        --dkg

[0] https://httpd.apache.org/mod_fcgid/


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