# 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.

- **Severity:** High 8.2 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 5 May 2026
- **Updated:** 5 May 2026
- **Also known as:** AZL-85715, BIT-modsecurity-2026-30923, DEBIAN-CVE-2026-30923, GHSA-qrjc-3jpc-3h2g, UBUNTU-CVE-2026-30923

## 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 (Out-of-bounds Read)

## Which versions are affected by CVE-2026-30923?

1 open source package ship an affected version, including modsecurity. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `modsecurity` | Bitnami | From 3.0.0 | 3.0.15 |

Products: Owasp Modsecurity.

## How do I fix CVE-2026-30923?

Upgrade modsecurity to 3.0.15 or later.

## 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](https://insights.sbomify.com/CVE-2026-52747/): Security feature bypass in ModSecurity (high 8.6)
- [CVE-2024-1019](https://insights.sbomify.com/CVE-2024-1019/): WAF bypass of the ModSecurity v3 release line (high 8.6)
- [CVE-2026-42268](https://insights.sbomify.com/CVE-2026-42268/): ModSecurity: Unsigned integer underflow in @verifySSN / @verifyCPF / @verifySVNR operators (high 8.2)
- [CVE-2025-48866](https://insights.sbomify.com/CVE-2025-48866/): ModSecurity has possible DoS vulnerability in sanitiseArg action (high 7.5)
- [CVE-2023-38285](https://insights.sbomify.com/CVE-2023-38285/): Trustwave ModSecurity 3.x before 3.0.10 has Inefficient Algorithmic Complexity. (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-30923 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-30923 exists.

Affected packages and fixed versions:
- modsecurity (Bitnami): affected from 3.0.0; fixed in 3.0.15

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-30923/ (Markdown: https://insights.sbomify.com/CVE-2026-30923/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-30923
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-30923
- OSV: https://osv.dev/vulnerability/CVE-2026-30923

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-30923/
Summaries are generated and may contain mistakes; the official description above is the record.