crypto/x509: Improper Certificate Validation
CVE-2026-27137 is a high-severity improper certificate validation vulnerability in crypto/x509 from Go standard library, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists version 1.26.1 as the first without the flaw, so updating crypto/x509 to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.66% chance of exploitation within 30 days, higher than 52% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update crypto/x509 to 1.26.1 or a later version.
- Read the advisory on pkg.go.dev for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
Version data comes from the organisation that assigned the CVE; 35 further products are omitted here. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- NoneNo data is disclosed.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by CNA.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.5 | High | CISA (ADP) |
| CVSS 3.1 | 7.5 | High | CNA |
Official description
When verifying a certificate chain which contains a certificate containing multiple email address constraints which share common local portions but different domain portions, these constraints will not be properly applied, and only the last constraint will be considered.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Certificate Validation
The product does not validate, or incorrectly validates, a certificate.
How developers prevent this class of flaw
- Certificates should be carefully managed and checked to assure that data are encrypted with the intended owner's public key.
- If certificate pinning is being used, ensure that all relevant properties of the certificate are fully validated before the certificate is pinned, including the hostname.
More Improper Certificate Validation vulnerabilities (CWE-295)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Patches and release notes
- groups.google.com/g/golang-announce/c/EdhZqrQ98hkRelease Notes
Other references
- go.dev/cl/752182Mailing List
- go.dev/issue/77952Issue Tracking
- access.redhat.com/errata/RHSA-2026:10125
- access.redhat.com/errata/RHSA-2026:10158
- access.redhat.com/errata/RHSA-2026:10169
- access.redhat.com/errata/RHSA-2026:10175
- access.redhat.com/errata/RHSA-2026:10184
- access.redhat.com/errata/RHSA-2026:10225
- access.redhat.com/errata/RHSA-2026:10250
- access.redhat.com/errata/RHSA-2026:10929
- access.redhat.com/errata/RHSA-2026:11800
- access.redhat.com/errata/RHSA-2026:13545
- access.redhat.com/errata/RHSA-2026:14879
- access.redhat.com/errata/RHSA-2026:19022
- access.redhat.com/errata/RHSA-2026:19049
Other vulnerabilities in crypto/x509
- 7.5 High severity
- 8.2 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
Recent Improper Certificate Validation vulnerabilities
- 7.5 High severity
- 8.1 High severity
- 7.4 High severity
- 7.4 High severity
- 9.1 Critical severity
- 8.1 High severity
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