GO-2026-4976 BIT-golang-2026-39825 CVE-2026-39825
ReverseProxy forwards queries with more than urlmaxqueryparams parameters in net/http/httputil
- Severity
- 5.3 / 10
- Medium · CVSS 3.1
- Exploit chance (EPSS)
- 0.39%
- Chance of exploitation in the next 30 days. Higher than 33.18% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- —
- Not classified
- Fix
1.26.3- Upgrade stdlib to this version or later
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.
Affected versions
Go
| Package | Vulnerable | Fixed in |
|---|---|---|
| stdlib | < 1.25.10>= 1.26.0-0, < 1.26.3 |
1.25.101.26.3 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
stdlib Go → 1.26.3
- go
go get stdlib@v1.26.3 && go mod tidy
Severity breakdown
CVSS 3.1 5.3
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- Low
- Integrity
- None
- Availability
- None
References
Advisories
Fixes and patches
Issue reports
Other links
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-4374-p667-p6c8 HTTP/2 rapid reset can cause excessive work in net/http | High Known exploited | Also affects stdlib |
| CVE-2020-0601 Certificate validation bypass on Windows in crypto/x509 | High Known exploited | Also affects stdlib |
| RUSTSEC-2026-0382 Distrust compromised intermediate certificates in crypto/x509 | Medium | Also affects stdlib |
| GO-2026-6613 HTTP/1 server connection desynchronization after 2xx CONNECT response in net/http | High | Also affects stdlib |
| GO-2026-6609 Lack of limit on size of parsed Range headers in net/http | High | Also affects stdlib |
| GO-2026-6608 Memory limit bypass when parsing MIME headers in net/textproto, mime/multipart | High | Also affects stdlib |
| GO-2026-6607 Reject malformed ECH outer extension references in crypto/tls | High | Also affects stdlib |
| GO-2026-6604 Root.Mkdir(All) can follow junctions out of the root on Windows in os | Critical | Also affects stdlib |
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