F5 NGINX JavaScript up to 1.0.0 XML module xml.exclusiveC14n out-of-bounds write

Summaryinfo

A vulnerability was found in F5 NGINX JavaScript up to 1.0.0 and classified as critical. This vulnerability affects the function xml.exclusiveC14n of the component XML module. Such manipulation leads to out-of-bounds write. This vulnerability is uniquely identified as CVE-2026-78689. The attack can be launched remotely. No exploit exists.

Detailsinfo

A vulnerability was found in F5 NGINX JavaScript up to 1.0.0 and classified as critical. Affected by this issue is the function xml.exclusiveC14n of the component XML module. The manipulation with an unknown input leads to a out-of-bounds write vulnerability. Using CWE to declare the problem leads to CWE-787. The product writes data past the end, or before the beginning, of the intended buffer. Impacted is confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at my.f5.com. This vulnerability is handled as CVE-2026-78689 since 08/26/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 09/02/2026).

Upgrading to version 1.0.1 eliminates this vulnerability.

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Productinfo

Type

• Web Server

Vendor

• F5

Name

• NGINX JavaScript

Version

• 1.0

License

• commercial

Website

• Vendor: https://f5.com/

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