CVE-2026-33810: When verifying a certificate chain containing excluded DNS constraints, these constraints are not correctly ap

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HIGH 8.2REMOTEUPGRADE

CVE-2026-33810 is a high-severity flaw (CVSS 8.2) affecting go. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

When verifying a certificate chain containing excluded DNS constraints, these constraints are not correctly applied to wildcard DNS SANs which use a different case than the constraint. This only affects validation of otherwise trusted certificate chains, issued by a root CA in the VerifyOptions.Roots CertPool, or in the system certificate pool.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	8.2 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.3% (top 73%)
CISA exploited list	No
Weakness	CWE-295, CWE-1289
Published	2026-04-08
Last modified	2026-09-18

Publisher (CNA): Go Project · Vendor: golang

Last updated 2026-09-18 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-08 02:16 UTCPublished CVE record published
2026-09-18 13:17 UTCUpdated Record last modified

golang go UPGRADE

Affected: >= 1.26.0 and < 1.26.2

Fixed in: 1.26.2

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 1.26.2 (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-2026-33810?

go: upgrade to 1.26.2. Exact commands for each OS are on this page.

Is CVE-2026-33810 being exploited?

CVE-2026-33810 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-2026-33810 affect?

CVE-2026-33810 affects go. Severity is high (CVSS 8.2). When verifying a certificate chain containing excluded DNS constraints, these constraints are not correctly applied to wildcard DNS SANs which use a different case than the constraint. This only affects validation of otherwise trusted certi

How urgent is CVE-2026-33810?

Priority 41/100. High severity; Remotely exploitable, no login, no user action

Software pages

Go (Golang) vulnerabilities

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References

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