CVE-2026-55203
HAProxy - Integer Overflow in FCGI Demux Record Length Field
7.5CVSSHIGH
Description
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 Vector Breakdown
Exploitability
AV:NAttack VectorNetwork
AC:HAttack ComplexityHigh
PR:NPrivileges RequiredNone
UI:NUser InteractionNone
Scope
S:CScopeChanged
Impact
C:LConfidentialityLow
I:HIntegrityHigh
A:NAvailabilityNone
Weaknesses
Affected Products
Attack Graph
Products CVE Techniques Tactics
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Exploitability
No known exploits, KEV entries, or remediation guidance available for this vulnerability yet.
MITRE ATT&CK
1 technique Initial Access
References
Timeline
Published
Jun 18, 2026
Last Updated
Jun 23, 2026
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