# CVE-2026-33810: Google Go crypto/x509 improper DNS constraint validation

Source: https://junglewise.ai/threats/cve-2026-33810-google-go-crypto-x509-improper-dns-constraint-validation  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-08. Updated: 2026-06-30  
License: CC BY 4.0 with a link back

CVE-2026-33810 · Severity: high · CVSS 8.2 · Published 2026-04-08

A vulnerability exists in the Go programming language's standard library used for verifying digital certificates. When a security policy is set to exclude certain domain names, the library fails to enforce these restrictions if the domain name uses a mix of uppercase and lowercase letters or includes a wildcard (like *.example.com). This could allow a malicious actor to use a certificate that should have been blocked, potentially leading to unauthorized access or the interception of sensitive data.

Technologies: [go (Go)](https://junglewise.ai/threats/technologies/go), [stdlib (Go)](https://junglewise.ai/threats/technologies/go-stdlib). Vendors: [Go](https://junglewise.ai/threats/vendors/go).

## Quick answers

**Is CVE-2026-33810 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-33810 being exploited in the wild.

**How severe is CVE-2026-33810?** High severity, with a CVSS score of 8.2, published 8 April 2026.

**Which products and versions are affected?** stdlib (Go) SEMVER:introduced=1.26.0-0,fixed=1.26.2.

**Is there a fix for CVE-2026-33810?** Yes. stdlib (Go): upgrade to 1.26.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-33810 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-33810?** 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 1.26.2 or later

  ```sh
  go get stdlib@v1.26.2
  ```


## Technical details

A vulnerability in the crypto/x509 package of the Go standard library (specifically Go 1.26) causes excluded DNS constraints to be bypassed. The root cause is an improper validation of equivalence (CWE-1289) where the library fails to correctly apply constraints to wildcard DNS Subject Alternative Names (SANs) when there is a case mismatch between the constraint and the SAN (e.g., 'EXAMPLE.COM' vs '*.example.com'). An attacker with a certificate issued by a trusted root CA can bypass name constraints intended to restrict the CA's scope. This affects certificate chains validated using VerifyOptions.Roots or the system certificate pool. The issue is fixed in Go 1.26.2.

## Affected products

- Google Go 1.26.0 to 1.26.1

## Identifiers

- CVE-2026-33810
- GO-2026-4866

## Timeline

- 2026-03-24: disclosed: Issue opened on Go GitHub repository
- 2026-04-07: advisory: Go project published vulnerability report GO-2026-4866
- 2026-04-08: patched: Go 1.26.2 released to address the issue

## References

- [https://pkg.go.dev/](https://pkg.go.dev/)
- [https://go.dev/cl/763763](https://go.dev/cl/763763)
- [https://go.dev/issue/78332](https://go.dev/issue/78332)
- [https://groups.google.com/g/golang-announce/c/0uYbvbPZRWU](https://groups.google.com/g/golang-announce/c/0uYbvbPZRWU)
- [https://pkg.go.dev/vuln/GO-2026-4866](https://pkg.go.dev/vuln/GO-2026-4866)
- [http://www.openwall.com/lists/oss-security/2026/04/19/4](http://www.openwall.com/lists/oss-security/2026/04/19/4)
- [http://www.openwall.com/lists/oss-security/2026/04/20/1](http://www.openwall.com/lists/oss-security/2026/04/20/1)

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