CVE-2026-78689: NGINX ngx_http_js_module vulnerablility
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 jsengine 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.
Affected Software
Event History
Frequently Asked Questions
Which deployments are realistically exposed?
Deployments are exposed when an affected NGINX configuration passes an externally controlled XML namespace prefix list to xml.exclusiveC14n(). The official nginxinc/nginx-saml reference implementation is affected during SAML signature verification because it processes InclusiveNamespaces/@PrefixList from untrusted SAML messages.
Does an attacker need a valid SAML signature to trigger the issue in the affected SAML reference implementation?
No. The prefix list is passed to xml.exclusiveC14n() before signature verification, so a valid signature is not required. A crafted SAML Response, Assertion, LogoutRequest, or LogoutResponse is sufficient.
How does the selected JavaScript engine affect the observed impact?
When js_engine is absent, NGINX uses the njs engine; exploitation corrupts adjacent objects and crashes the NGINX worker. With the QuickJS engine, each affected call also leaks the prefix list, causing worker memory usage to grow across requests.