ModSecurity CVE-2026-104259

Exploitation requires that the target runs a ModSecurity deployment whose ruleset applies the t:removeComments transformation action during input normalization (common in configurations derived from the OWASP Core Rule Set). The bypass only yields real impact when there is an exploitable downstream sink (e.g., SQLi/XSS/command injection) that the WAF was the control relied upon to block. Limiting factors: the flaw affects only rules/chains that invoke removeComments, so configurations not using that transformation are unaffected; and where ModSecurity is one layer among several controls, the effective risk is reduced to loss of that single filtering layer rather than a full protection failure. Authentication requirements not confirmed from available data (no CVSS vector provided).

Nearly all standard risk signals are MISSING from the input: CVSS score and vector are N/A, and no EPSS, KEV, POC, or SSVC data was provided - so exploitation probability, active-exploitation status, and automatability cannot be quantified from the data at hand. The vulnerability class itself is a security-control bypass rather than a direct compromise: per the description, the t:removeComments transformation mishandles the character immediately following a comment terminator, which allows crafted input to survive normalization and thereby 'bypass rules.' The t:removeComments transformation is ModSecurity-specific syntax, so this is most likely a WAF/ruleset evasion flaw in ModSecurity (INFERRED, not confirmed - see confidence_notes). Real-world priority is therefore conditional: this is not a standalone high-CVSS RCE, but a defense-in-depth weakening that matters a great deal to organizations relying on ModSecurity/OWASP CRS as a primary filter in front of injection-prone applications, and much less where the WAF is only one layer. With no EPSS or KEV to corroborate urgency, treat this as a patch-on-normal-cycle security-bypass issue unless the referenced GHSA-qrch-pjfr-9g47 indicates otherwise. Note explicitly: CVSS is absent, so attack vector and privilege requirements below are assessed independently, not copied from vendor scoring.

An attacker sends an HTTP request containing a payload (e.g., SQL injection or XSS) wrapped so that a mishandled character follows a comment terminator; the removeComments transformation normalizes the value incorrectly, so the WAF ruleset inspects a benign-looking string while the backend receives the live payload. This smuggles the malicious input past the protection layer, enabling exploitation of a downstream injection flaw. No public exploit identified at time of analysis, and the referenced GHSA advisory content was not included in the input.