# CVE-2026-33811: Go net package double-free in cgo DNS resolver

Source: https://junglewise.ai/threats/cve-2026-33811-go-net-package-double-free-in-cgo-dns-resolver  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-07. Updated: 2026-06-30  
License: CC BY 4.0 with a link back

CVE-2026-33811 · Severity: high · CVSS 7.5 · Published 2026-05-07

A vulnerability in the Go programming language's networking library can cause applications to crash when they attempt to resolve certain domain names. This occurs when a malicious or malformed DNS response contains an excessively long CNAME record, leading to a memory error that terminates the program. This can be used by attackers to cause a denial-of-service, potentially taking down critical web services or internal applications that rely on Go's standard networking features.

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

## Quick answers

**Is CVE-2026-33811 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-33811 being exploited in the wild.

**How severe is CVE-2026-33811?** High severity, with a CVSS score of 7.5, published 7 May 2026.

**Which products and versions are affected?** stdlib (Go) SEMVER:introduced=0,fixed=1.25.10,introduced=1.26.0-0,fixed=1.26.3.

**Is there a fix for CVE-2026-33811?** Yes. stdlib (Go): upgrade to 1.26.3 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-33811 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-33811?** Check whether you run 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 1.26.3 or later

  ```sh
  go get stdlib@v1.26.3
  ```


## Technical details

A double-free vulnerability (CWE-415) exists in the Go standard library 'net' package when using the cgo-based DNS resolver. The flaw is located within the LookupCNAME and Resolver.LookupCNAME functions. When the resolver processes a specially crafted, excessively long CNAME DNS response, it incorrectly manages C memory pointers, leading to a double-free condition and a subsequent process crash. This is a remote attack vector requiring no authentication, as an attacker only needs to control or spoof a DNS response sent to the vulnerable application. The issue is resolved in Go versions 1.25.10 and 1.26.3.

## Affected products

- Google Go before 1.25.10, 1.26.0 before 1.26.3
- Red Hat Red Hat Hardened Images 1
- Red Hat Red Hat OpenShift Service Mesh 3.0, 3.1, 3.2, 3.3

## Identifiers

- CVE-2026-33811
- GO-2026-4981

## Timeline

- 2026-04-16: disclosed: Issue opened on Go GitHub repository
- 2026-05-07: advisory: Go vulnerability report GO-2026-4981 published
- 2026-05-07: patched: Fixes released in Go 1.25.10 and 1.26.3
- 2026-06-04: patched: Red Hat released security advisories for affected products

## References

- [https://pkg.go.dev/](https://pkg.go.dev/)
- [https://go.dev/cl/767860](https://go.dev/cl/767860)
- [https://go.dev/issue/78803](https://go.dev/issue/78803)
- [https://groups.google.com/g/golang-announce/c/qcCIEXso47M](https://groups.google.com/g/golang-announce/c/qcCIEXso47M)
- [https://pkg.go.dev/vuln/GO-2026-4981](https://pkg.go.dev/vuln/GO-2026-4981)
- [https://access.redhat.com/errata/RHSA-2026:23262](https://access.redhat.com/errata/RHSA-2026:23262)
- [https://access.redhat.com/errata/RHSA-2026:23264](https://access.redhat.com/errata/RHSA-2026:23264)

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