CVE-2026-39825: ReverseProxy can forward queries containing parameters not visible to Rewrite functions

Routine

MEDIUM 5.3REMOTEUPGRADE

CVE-2026-39825 is a medium-severity flaw (CVSS 5.3) affecting go. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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

Why this priority

Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	5.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.4% (top 67%)
CISA exploited list	No
Published	2026-05-07
Last modified	2026-10-26

Publisher (CNA): Go Project · Vendor: golang

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-05-07 20:16 UTCPublished CVE record published
2026-10-26 20:10 UTCUpdated Record last modified

golang go UPGRADE

Affected: < 1.25.10 · >= 1.26.0 and < 1.26.3

Fixed in: 1.25.10, 1.26.3

Safe to downgrade to: a release before 1.26.0

1. Check installed version

apt-cache policy go || rpm -q go || go --version

2. UPGRADE to 1.25.10 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade go

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade go

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 1.26.0 (Debian / Ubuntu)

apt-cache madison go sudo apt install go=<VERSION_BEFORE_1.26.0> sudo apt-mark hold go

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list go sudo dnf downgrade go-<VERSION_BEFORE_1.26.0> sudo dnf versionlock add go

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-39825?

go: upgrade to 1.25.10, 1.26.3. Exact commands for each OS are on this page.

Is CVE-2026-39825 being exploited?

CVE-2026-39825 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-39825 affect?

CVE-2026-39825 affects go. Severity is medium (CVSS 5.3). 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 p

How urgent is CVE-2026-39825?

Priority 32/100. Remotely exploitable, no login, no user action

Software pages

Go (Golang) vulnerabilities

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References

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