ReverseProxy forwards queries with more than urlmaxqueryparams parameters in net/http/httputil

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Summary

CVECVE-2026-39825
StatePUBLISHED
AssignerGo
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-05-07 20:16:43 UTC
Updated2026-05-08 22:16:29 UTC
DescriptionReverseProxy 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.

Risk And Classification

Primary CVSS: v3.1 5.3 MEDIUM from ADP

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

EPSS: 0.000120000 probability, percentile 0.018830000 (date 2026-05-12)

Problem Types: CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

VersionSourceTypeScoreSeverityVector
3.1ADPDECLARED5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
3.1134c704f-9b21-4f2e-91b3-4a467353bcc0Secondary5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Go Standard Library Net/http/httputil affected 1.25.10 semver Not specified
CNA Go Standard Library Net/http/httputil affected 1.26.0-0 1.26.3 semver Not specified

References

ReferenceSourceLinkTags
go.dev/issue/78948 [email protected] go.dev
go.dev/cl/770541 [email protected] go.dev
pkg.go.dev/vuln/GO-2026-4976 [email protected] pkg.go.dev
groups.google.com/g/golang-announce/c/qcCIEXso47M [email protected] groups.google.com
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