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High-Severity ModSecurity Vulnerabilities Allow WAF Bypass

High-Severity ModSecurity Vulnerabilities Allow WAF Bypass

First seen 9 Nov 2026, 16:14 UTC • •
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ThreatCluster AI
ThreatCluster •November 9, 2026 at 16:15 UTC
  • •Two high-severity vulnerabilities in ModSecurity disclosed on November 5, 2026.
  • •CVE-2026-104269 allows WAF bypass leading to potential remote code execution.
  • •Administrators should upgrade to version 3.0.17 and validate file uploads.

Two high-severity vulnerabilities in ModSecurity, tracked as CVE-2026-104269 and CVE-2026-73857, were disclosed on November 5, 2026. CVE-2026-104269 allows attackers to bypass file upload restrictions due to a parser mismatch in the multipart parser, affecting versions 3.0.0 and later. The flaw can lead to remote code execution if an attacker sends a crafted HTTP request. CVE-2026-73857 involves an uninitialized pointer dereference that could lead to denial of service or memory disclosure, affecting versions 3.0.15 and 3.0.16. Administrators are urged to upgrade to version 3.0.17 and implement server-side validation for file uploads. Proof-of-concept exploit code for CVE-2026-104269 is publicly available. The vulnerabilities highlight the parser-differential problem seen in web application firewalls.

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Timeline

2026-11-05
CVE-2026-104269 published
Disclosed vulnerability allows bypass of file upload restrictions in ModSecurity.
Hkcert
2026-11-05
CVE-2026-73857 published
Disclosed vulnerability involves uninitialized pointer dereference in ModSecurity.
Gbhackers

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Common questions

Which versions of ModSecurity are affected?
ModSecurity versions 3.0.0 and later, but earlier than 3.0.17 are affected by CVE-2026-104269.
Is there a patch available?
Yes, version 3.0.17 addresses the vulnerabilities, and administrators should upgrade to this version.
What immediate actions should be taken?
Administrators should upgrade to version 3.0.17 and implement server-side validation for file uploads.