Is CVE-2026-27137 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-27137 being exploited in the wild.

How severe is CVE-2026-27137?

High severity, with a CVSS score of 7.5, published 6 March 2026.

Which products and versions are affected?

stdlib (Go) SEMVER:introduced=1.26.0-0,fixed=1.26.1.

Is there a fix for CVE-2026-27137?

Yes. stdlib (Go): upgrade to 1.26.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

How is CVE-2026-27137 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-27137?

Check whether you run go (Go) or stdlib (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-27137: Google Go crypto/x509 improper certificate validation in email constraints

CVE-2026-27137 · Severity: high · CVSS 7.5 · Published 2026-03-06

A security issue was identified in the Go programming language's standard library used for verifying digital certificates. When a certificate contains multiple email address restrictions that look similar (sharing the same username but different domains), the system may fail to enforce all of them, potentially allowing unauthorized email addresses to be accepted. This could allow a malicious actor with a certificate from a trusted provider to bypass specific security constraints intended to limit their authority.

Technologies: go (Go), stdlib (Go). Vendors: Go.

Quick answers

Is CVE-2026-27137 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-27137 being exploited in the wild.
How severe is CVE-2026-27137?: High severity, with a CVSS score of 7.5, published 6 March 2026.
Which products and versions are affected?: stdlib (Go) SEMVER:introduced=1.26.0-0,fixed=1.26.1.
Is there a fix for CVE-2026-27137?: Yes. stdlib (Go): upgrade to 1.26.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is CVE-2026-27137 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-27137?: Check whether you run go (Go) or stdlib (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

stdlib (Go): upgrade to 1.26.1 or later
```
go get stdlib@v1.26.1
```

Technical details

A vulnerability exists in the crypto/x509 package of the Go standard library during certificate chain validation. When a certificate contains multiple email address name constraints that share a common local portion (the part before the '@') but have different domain portions, the validation logic only applies the final constraint in the list. This flaw allows certificates containing email addresses that should be excluded or are not permitted by the intermediate constraints to be successfully returned by Certificate.Verify. The issue is specific to Go 1.26 and requires a trusted CA to issue the non-compliant certificate, as name constraint checks occur after the chain is built to a trusted root. The vulnerability was addressed in Go 1.26.1.

Affected products

Google Go 1.26.0 to 1.26.1

Identifiers

CVE-2026-27137
GO-2026-4599

Timeline

2026-03-04: disclosed: Issue reported to the Go project by Jakub Ciolek.
2026-03-06: advisory: Published as GO-2026-4599 and CVE-2026-27137.
2026-03-06: patched: Fixed in Go version 1.26.1.

References

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