What’s Vulnerable › Vulnerabilities

CVE-2026-97031: Reject malformed ECH outer extension references in crypto/tls

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-08 · updated 2026-10-09
• Weakness: CWE-405

Description

Multiple ECH outer extension references are not permitted under RFC 9849; previously, a client could send a well-crafted packet that could trigger memory exhaustion in the server process by specifying multiple references. We now reject these as malformed and curb the memory amplification vector as a result.

Affected products

• Go Stdlib: before 1.26.9; from 1.27.0-0 before 1.27.2 — fixed in 1.26.9, 1.27.2
• Go standard library crypto/tls: before 1.26.9; from 1.27.0-0 before 1.27.2 — fixed in 1.26.9, 1.27.2

How to fix

Upgrade to a fixed version: Go Stdlib 1.26.9, 1.27.2; Go standard library crypto/tls 1.26.9, 1.27.2. Check the vendor advisory for mitigations.

References

• https://go.dev/cl/847312
• https://go.dev/issue/81855
• https://groups.google.com/g/golang-announce/c/U2fTuyDJznI
• https://pkg.go.dev/vuln/GO-2026-6607

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