Thecyberexpress

Cloudflare Patches Critical WAF Bypass Vulnerability

First seen 21 Jan 2026, 06:39 UTC •

•88% similarity •21.0

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Cloudflare addressed a critical zero-day vulnerability in its Web Application Firewall (WAF) that allowed attackers to bypass security rules and access protected origin servers. Discovered by FearsOff security researchers in October, the flaw stemmed from a logic error in the ACME certificate validation process. Cloudflare confirmed that no customer action was required to mitigate the issue.

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Attack Flow

11 entities, 16 inferred relationships (STIX 2.1).

Technique (2)

Data Breach
Zero-day Exploit

Organization (2)

Cloudflare
FearsOff

Affected Platform (5)

Http-01
PHP
Spring
Tomcat
Web Application Firewall

Tool (1)

ACME

Vulnerability (1)

Path Traversal

Relationships

ACME exploits Path Traversal
Path Traversal targets Http-01
Path Traversal targets PHP
Path Traversal targets Spring
Path Traversal targets Tomcat
Data Breach targets Http-01
Data Breach targets PHP
Data Breach targets Spring
Data Breach targets Tomcat
Zero-day Exploit targets Http-01
Zero-day Exploit targets PHP
Zero-day Exploit targets Spring
Zero-day Exploit targets Tomcat
Path Traversal related to Cloudflare
Path Traversal related to FearsOff
Path Traversal related to Web Application Firewall

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Tracked Entities in This Story

Cloudflare FearsOff Http-01 PHP Spring Tomcat Web Application Firewall

Cloudflare Patches Critical WAF Bypass Vulnerability

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Defensive Countermeasures

Extracted Entities

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