# CVE-2026-97031: Go crypto/tls malformed ECH extension DoS

Source: https://junglewise.ai/threats/cve-2026-97031-go-2026-6607-reject-malformed-ech-outer-extension-references-in  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-08. Updated: 2026-10-10  
License: CC BY 4.0 with a link back

CVE-2026-97031 · Severity: high · CVSS 7.5 · Published 2026-10-08

Go's crypto/tls library, which handles encrypted client hello (ECH) negotiation in TLS connections, accepts malformed extension references that violate the ECH specification. An attacker can send a crafted packet with multiple ECH outer extension references to trigger memory exhaustion in the server, causing a denial of service.

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-2026-97031 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-97031 being exploited in the wild.

**How severe is CVE-2026-97031?** High severity, with a CVSS score of 7.5, published 8 October 2026.

**Which products and versions are affected?** go (Go) <UNKNOWN>; stdlib (Go) SEMVER:introduced=0,fixed=1.26.9,introduced=1.27.0-0,fixed=1.27.2.

**Is there a fix for CVE-2026-97031?** Yes. stdlib (Go): upgrade to 1.27.2 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-97031 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-97031?** 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 1.27.2 or later

  ```sh
  go get stdlib@v1.27.2
  ```


## Technical details

The vulnerability is a denial-of-service issue in Go's crypto/tls ECH handling where multiple ECH outer extension references—which are not permitted under RFC 9849—are not rejected, allowing a remote attacker to exhaust server memory through a memory amplification vector. The fix rejects malformed ECH packets with multiple extension references as invalid.

## Affected products

- Go Go <UNKNOWN>

## Identifiers

- CVE-2026-97031
- GO-2026-6607

## Timeline

- 2026-10-08: disclosed

## References

- [https://go.dev/cl/847312](https://go.dev/cl/847312)
- [https://go.dev/issue/81855](https://go.dev/issue/81855)

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