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.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-78689?
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
Which versions are affected by CVE-2026-78689?
How do I fix CVE-2026-78689?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-78689 being exploited?
There is no known exploitation of CVE-2026-78689 in the wild and no public exploit code.
Sources
Also known as AZL-99297, DEBIAN-CVE-2026-78689, GHSA-3gxx-pmrm-ghvv, UBUNTU-CVE-2026-78689.