CVE-2026-55203HAProxy through 3.4.0, fixed in commit 5985276, contains an integer overflow vulnerability in the fcgi_conn structure's drl field that allows buffer misparse as new FCGI record headers.
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HAProxy through 3.4.0, fixed in commit 5985276, contains an integer overflow vulnerability in the fcgi_conn structure's drl field that allows buffer misparse as new FCGI record headers. When contentLength is 65535 and paddingLength is 1 or more, the drl field wraps to 0, causing incorrect record consumption and allowing malicious FastCGI backends to desynchronize the FCGI framing parser, potentially causing request routing errors, response smuggling, or memory safety issues.
- CVSS
- 9.1 CRITICAL (v3.1, NVD)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
- Weakness (CWE)
- CWE-190
- Known exploited
- Not in CISA's KEV catalog
- EPSS (exploitation in the next 30 days)
- Not loaded for this CVE
- Assigned by
- Not given
- NVD analysis
- Analyzed
- Record last updated
- Oct 8, 2026
- First seen by InfoSec Signals
- Oct 9, 2026
Affected products
haproxy haproxy haproxy:haproxy | before 2.4.36; from 2.5 before 2.6.30; from 2.7 before 2.8.25; from 2.9 before 3.0.24; from 3.1 before 3.2.20; from 3.3 before 3.4.1 | NVD |
References
- https://github.com/haproxy/haproxy/commit/5985276735777634d8c85f1d73bb7764aab0d6ddpatch
- https://www.vulncheck.com/advisories/haproxy-integer-overflow-in-fcgi-demux-record-length-fieldthird-party-advisory
The CVE record on cve.org NVD's entry
The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.