Vulnerability in Golang Go
CVE-2026-39825
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.3 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N.
EPSS exploit prediction
EPSS: 0.004 (33.0th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 33rd percentile — 33.0% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: +0.000
Affected products
- Golang Go
- Go Standard Library Net/http/httputil — versions 0, 1.26.0-0
References
- go.dev/cl/770541 (Patch)
- go.dev/issue/78948 (Issue Tracking)
- groups.google.com/g/golang-announce/c/qcCIEXso47M (Release Notes)
- pkg.go.dev/vuln/GO-2026-4976 (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-39825?
- CVE-2026-39825 is a medium-severity vulnerability in Golang Go, classified under CWE-444: INCONSISTENT INTERPRETATION OF HTTP REQUESTS ('HTTP REQUEST/RESPONSE SMUGGLING'). CVSS score: 5.3/10. Published 2026-05-07.
- How severe is CVE-2026-39825?
- Medium severity. CVSS v3 base score is 5.3 out of 10.