October 30, 2026

CVE Watchtower

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CVE-2026-55203NVD

Vulnerability Summary

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.
Severity Level
HIGH(7.5)
Published Date
Jun 18, 2026
Last Modified
Jul 14, 2026
Exploitation Status
No confirmed exploitation yet
EPSS Score (30-Day)
0.35%Probability
Root Weakness (CWE)
CWE-190: Unknown/Unlisted Weakness ↗
Refer to the official MITRE database for detailed architectural specifications regarding this weakness.
CVSS v4.0 Base Metrics — Score 9.0 (CRITICAL)
Attack VectorNetwork
Attack ComplexityLow
Attack RequirementsPresent
Privileges RequiredNone
User InteractionNone
Confidentiality (Vulnerable System)None
Integrity (Vulnerable System)High
Availability (Vulnerable System)None
Confidentiality (Subsequent System)Low
Integrity (Subsequent System)High
Availability (Subsequent System)None
CVSS v3.1 Base Metrics — Score 7.5 (HIGH)
Attack VectorNetwork
Attack ComplexityHigh
Privileges RequiredNone
User InteractionNone
ScopeChanged
ConfidentialityLow
IntegrityHigh
AvailabilityNone

Affected & Patched Versions

Affected Versions
  • haproxy haproxy <= 3.4.0
Patched Versions
  • haproxy haproxy 3.4.0
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🎁7-Day Free Trial — Try Pro or Team, no card required.
📧Email Delivery — Threat intel straight to your inbox.
♾️Unlimited Vendors — Track your entire stack.
🚨All New CVEs — Be the first to know.
📈EPSS Spike Alerts — Catch rising risk before it peaks.
🎯Custom EPSS/CVSS — Filter noise, focus on risk.
🛡️Exploit Intel — A 2nd confirmed-exploit signal beyond KEV.
🐙GitHub Issues — Auto-tracked, no duplicates.
📬Weekly Digest — One clean summary, not inbox spam.
🏷️Watchlist Groups — Tag alerts by team (Infra/AppSec/SOC).
💬Webhooks — Slack & Teams integration.
🔀Smart Routing — Critical alerts to one channel, rest to another.
🚫Ad-Free — Uninterrupted experience.

External References