Integer overflow in Haproxy
CVE-2026-55203
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.
Vulnerability class: Integer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:H/A:N.
EPSS exploit prediction
EPSS: 0.006 (45.3th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 45th percentile — 45.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.006 · change: +0.002
Affected products
- Haproxy — versions 0, 5985276735777634d8c85f1d73bb7764aab0d6dd
Weakness classification (CWE)
References
- github.com/haproxy/haproxy/commit/5985276735777634d8c85f1d73bb7764aab0d6dd (Patch, patch)
- www.vulncheck.com/advisories/haproxy-integer-overflow-in-fcgi-demux-record-leng… (Third Party Advisory, third-party-advisory)
Frequently asked questions
- What is CVE-2026-55203?
- CVE-2026-55203 is a high-severity vulnerability in Haproxy, classified under Integer Overflow or Wraparound. CVSS score: 7.5/10. Published 2026-06-18.
- How severe is CVE-2026-55203?
- High severity. CVSS v3 base score is 7.5 out of 10.