CVE-2026-30923 libModSecurity3 denial of service via segfault when using t:hexDecode on single-character query strings
An attacker can crash web server worker processes by sending single-character query strings to rules using hexDecode, causing a denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-30923?
CVE-2026-30923 is a high-severity denial of service vulnerability in owasp-modsecurity ModSecurity, published on 5 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-125
Which versions are affected by CVE-2026-30923?
1 open source package ship an affected version, including modsecurity. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
modsecurity Bitnami | From 3.0.0 | 3.0.15 |
Products include Owasp Modsecurity.
How do I fix CVE-2026-30923?
Upgrade modsecurity to 3.0.15 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-30923 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-30923 exists.
Other vulnerabilities in owasp-modsecurity ModSecurity
- CVE-2026-52747 Security feature bypass in ModSecurity
- CVE-2024-1019 WAF bypass of the ModSecurity v3 release line
- CVE-2026-42268 ModSecurity: Unsigned integer underflow in @verifySSN / @verifyCPF / @verifySVNR operators
- CVE-2025-48866 ModSecurity has possible DoS vulnerability in sanitiseArg action
- CVE-2023-38285 Trustwave ModSecurity 3.x before 3.0.10 has Inefficient Algorithmic Complexity.
Sources
Also known as AZL-85715, BIT-modsecurity-2026-30923, DEBIAN-CVE-2026-30923, GHSA-qrjc-3jpc-3h2g, UBUNTU-CVE-2026-30923.