CVE-2009-1891: The mod_deflate module in Apache httpd 2.2.11 and earlier compresses large files until completion even afte...

Security readout for executives and security teams

A remote request can make affected Apache httpd servers keep compressing large files even after the client disconnects. That wastes CPU and can degrade or deny service. The issue is old, but unpatched legacy servers or appliances may still be exposed. Most relevant exposure is legacy Apache httpd 2.2.11 or earlier with mod_deflate enabled, especially systems serving large compressible files. Vendor advisories show multiple Linux and Unix distributors tracked the issue, but current exposure depends on local package age and configuration. Schedule remediation for legacy internet-facing Apache systems, especially where availability is business-critical. This is not described as data compromise, but CPU exhaustion can still affect customer-facing services. Modern patched fleets are likely lower priority after inventory confirmation. Mitigation focus: Identify Apache httpd versions at or below 2.2.11.; Apply applicable vendor httpd security updates from your OS or appliance vendor.; Check vendor guidance before disabling or constraining mod_deflate as a workaround..

Prepared

Jun 28, 2026, 10:45 UTC (UTC+00:00)

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.