CVE-2026-39825: ReverseProxy forwards queries with more than urlmaxqueryparams parameters in net/http/httputil
ReverseProxy can forward queries containing parameters not visible to Rewrite functions. When used with a Rewrite function, or a Director function which parses query parameters, ReverseProxy sanitizes the forwarded request to remove query parameters which are not parsed by url.ParseQuery. ReverseProxy does not take ParseQuery's limit on the total number of query parameters (controlled by GODEBUG=urlmaxqueryparams=N) into account. This can permit ReverseProxy to forward a request containing a query parameter that is not visible to the Rewrite function. For example, the query "a1=x&a2=x&...&a10000=x&hidden=y" can forward the parameter "hidden=y" while hiding it from the proxy's Rewrite function.
Affected Software
Remediation
Patch Available
Event History
Frequently Asked Questions
What is the severity of CVE-2026-39825?
CVE-2026-39825 is considered to have medium severity due to potential exposure of sensitive data through improper query parameter handling.
How do I fix CVE-2026-39825?
To fix CVE-2026-39825, update to the latest version of Go that includes the necessary patches for the net/http/httputil ReverseProxy.
What are the potential exploits of CVE-2026-39825?
CVE-2026-39825 can be exploited to reveal query parameters that should otherwise be hidden, leading to unintended information disclosure.
Which software is affected by CVE-2026-39825?
CVE-2026-39825 affects the net/http/httputil ReverseProxy component of the Go standard library.
Is CVE-2026-39825 an issue with all versions of Go?
CVE-2026-39825 is present in certain versions of the Go standard library, so it is important to check the specific version for exposure.