# CVE-2026-78689: NGINX ngx_http_js_module vulnerablility

> Remote attackers can cause denial of service or potentially execute code via out-of-bounds write in NGINX JavaScript XML parser when processing untrusted SAML messages.

- **Severity:** Critical 9.2 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/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:** 2 Sep 2026
- **Updated:** 3 Sep 2026
- **Also known as:** AZL-99297, DEBIAN-CVE-2026-78689, GHSA-3gxx-pmrm-ghvv, UBUNTU-CVE-2026-78689

## What is CVE-2026-78689?

CVE-2026-78689 is a critical memory corruption vulnerability in F5 NGINX JavaScript, published on 2 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Description

NGINX JavaScript (njs) has a vulnerability in the XML module's namespace prefix list parser, reachable through the xml.exclusiveC14n() method. An unauthenticated remote attacker can trigger it when an affected NGINX configuration passes an externally controlled XML namespace prefix list to that method. Both the njs and the QuickJS (qjs) engines are affected. A crafted prefix list causes an out-of-bounds write past the end of a heap allocation. With the njs engine, which is the engine used when the js_engine directive is absent, this corrupts adjacent objects and crashes the NGINX worker. With the QuickJS engine, the same call additionally leaks the prefix list on every invocation, causing worker memory to grow across requests. The official nginxinc/nginx-saml reference implementation is affected during SAML signature verification. It reads InclusiveNamespaces/@PrefixList from an untrusted SAML message and passes it to xml.exclusiveC14n() before the signature has been verified, so a valid SAML signature is not required. A crafted SAML Response, Assertion, LogoutRequest, or LogoutResponse is sufficient. Code execution has not been demonstrated and cannot be ruled out for all platforms, as the effect of the out-of-bounds write depends on conditions beyond the attacker's control.  

 Impact

This vulnerability allows remote attackers to cause a denial of service on the NGINX system, either through repeatable worker restarts or through worker memory growth or possibly trigger code execution. There is no control plane exposure; this is a data plane issue only.

Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

Weakness: CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2026-78689?


## How do I fix CVE-2026-78689?

Apply the vendor's patch.

## Is CVE-2026-78689 being exploited?

There is no known exploitation of CVE-2026-78689 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-78689 and fix it if it is affected.

What it is: CVE-2026-78689 is a critical memory corruption vulnerability in F5 NGINX JavaScript, published on 2 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-78689 in the wild and no public exploit code.

Affected product: F5 NGINX JavaScript. No package-level version data is available, so check the vendor advisory linked from the reference page.

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-2026-78689/ (Markdown: https://insights.sbomify.com/CVE-2026-78689/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-78689
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-78689
- OSV: https://osv.dev/vulnerability/CVE-2026-78689

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From sbomify Insights: https://insights.sbomify.com/CVE-2026-78689/
Summaries are generated and may contain mistakes; the official description above is the record.