PatchSiren

PatchSiren cyber security CVE debrief

CVE-2026-9658 RRWO CVE debrief

Plack::Middleware::Security::Common versions before 0.13.1 for Perl did not block header injections in request paths. The header injection rule was ineffective at blocking header injections in the request paths unless they were double-encoded. The vulnerability was published on 2026-05-28 and modified later the same day. The vendor is identified as RRWO based on Metacpan reference data, though confidence is low and review is needed. No CVSS score or severity is currently assigned. The weakness types associated are CWE-113 (Improper Neutralization of CRLF Sequences in HTTP Headers) and CWE-790.

Vendor
RRWO
Product
Plack::Middleware::Security::Common
CVSS
Unknown
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-28
Original CVE updated
2026-05-29
Advisory published
2026-05-28
Advisory updated
2026-05-29

Who should care

Organizations running Perl web applications using Plack::Middleware::Security::Common versions prior to 0.13.1, particularly those exposed directly to the internet or behind reverse proxies that may forward malformed request paths.

Technical summary

The Plack::Middleware::Security::Common middleware for Perl, prior to version 0.13.1, contained an ineffective header injection protection mechanism. The vulnerability allowed HTTP header injection through request paths containing CRLF sequences, but only when those sequences were double-encoded. Single-encoded CRLF injections in paths were not blocked as intended. The security implication is potential HTTP request smuggling or response splitting attacks, though the actual exploitability depends on how reverse proxies and Plack-based servers process such malformed request paths. The fix in version 0.13.1 addresses this bypass condition.

Defensive priority

medium

Recommended defensive actions

  • Upgrade Plack::Middleware::Security::Common to version 0.13.1 or later
  • Review application logs for suspicious request paths containing CRLF sequences
  • Validate that reverse proxy configurations properly handle and sanitize request paths with embedded header sequences
  • Consider implementing additional input validation at the application layer for path components

Evidence notes

CVE published 2026-05-28T13:16:25.067Z; modified 2026-05-28T23:16:45.050Z. Vendor attribution to RRWO from Metacpan reference with low confidence. Weaknesses: CWE-113, CWE-790.

Official resources

2026-05-28