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© 2026 FAUCET Technologies LLC. All rights reserved.

CVE-2026-55203

38
FAUCET Score

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.

First published: Jun 18, 2026Last modified: Jul 14, 2026

Impacted Technologies

VendorProductVersion(s)CPE
<= 3.4.0CPE matchmatch criteria
cpe:2.3:a:haproxy:haproxy:*:*:*:*:*:*:*:*
>= 0, <= 3.4.0CPE match
cpe:2.3:a:haproxy:haproxy:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 4.0

9.0CRITICAL

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:L/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Attack Vector
NETWORK
Attack Complexity
LOW
Attack Requirements
PRESENT
Privileges Required
NONE
User Interaction
NONE
VS Confidentiality
NONE
VS Integrity
HIGH
VS Availability
NONE
SS Confidentiality
LOW
SS Integrity
HIGH
SS Availability
NONE
Exploit Maturity
NOT_DEFINED
CvssVersion
4.0

Exploit Intelligence

EPSS Score
0.35%
Probability of exploitation in next 30 days
EPSS Percentile
27.3%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0035 is in the 5th percentile among its peer group of 36,862 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (5)

github_advisorypatch availablevia nvd_reference
View patch
microsoftpatch availablevia msrc
Product: azl3 haproxy 2.9.11-6 on Azure Linux 3.0Fixed in: 2.9.11-7
microsoftpatch availablevia msrc
Product: azl3 haproxy 2.9.11-7 on Azure Linux 3.0Fixed in: 2.9.11-7
microsoftpatch availablevia msrc
Product: 21468-17084Fixed in: 2.9.11-7
microsoftpatch availablevia msrc
Product: 21525-17084Fixed in: 2.9.11-7

Vendor Advisories (1)

microsoft2026-Jun/CVE-2026-55203Important

HAProxy - Integer Overflow in FCGI Demux Record Length Field

Jun 9, 2026

References

github.com / haproxy/haproxy/commit/5985276735777634d8c85f1d73bb7764aab0d6dd
Patch
vulncheck.com / advisories/haproxy-integer-overflow-in-fcgi-demux-record-length-field
Third Party Advisory