CVE-2026-30923: libModSecurity3 denial of service via segfault when using t:hexDecode on single-character query strings
ModSecurity is an open source, cross platform web application firewall (WAF) engine for Apache, IIS and Nginx. Libmodsecurity is one component of the ModSecurity v3 project. A segmentation fault occurs when a rule using the t:hexDecode transformation inspects a query string parameter containing a single character. An attacker can exploit this to crash worker processes, causing a denial of service. Service resumes once the attack stops as worker processes recover from the segfault. All versions before 3.0.15 of libModSecurity3 are affected. This has been patched in version 3.0.15.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
libModSecurity3to a version that resolves this vulnerability.Fixed in 3.0.15
Event History
Frequently Asked Questions
What is the severity of CVE-2026-30923?
CVE-2026-30923 is a high severity vulnerability that allows denial of service due to a segmentation fault.
How do I fix CVE-2026-30923?
To fix CVE-2026-30923, upgrade to libModSecurity3 version 3.0.15 or later.
What systems are affected by CVE-2026-30923?
CVE-2026-30923 affects libModSecurity3 versions earlier than 3.0.15 in ModSecurity implementations.
What is the impact of CVE-2026-30923?
The impact of CVE-2026-30923 is the potential for denial of service through application crashes.
When was CVE-2026-30923 published?
CVE-2026-30923 was published in 2026 as part of an advisory regarding the vulnerability in libModSecurity3.