Vulnerability in Rustls
CVE-2026-123611
rustls before 0.23.46 contains a key exchange downgrade vulnerability that allows network attackers to poison the per-server-name key-exchange group record via an unauthenticated ServerHello. Attackers can answer one connection with a ServerHello selecting X25519, causing later ClientHellos to send only classical shares and lose post-quantum confidentiality.
Published .
CVSS v3 metric
CVSS v3 base score 3.7 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
Weakness classification (CWE)
References
- github.com/rustls/rustls/security/advisories/GHSA-w44r-93j7-qv28 (vendor-advisory)
- www.vulncheck.com/advisories/rustls-before-0.23.46-key-exchange-downgrade-via-u… (third-party-advisory)
Frequently asked questions
- What is CVE-2026-123611?
- CVE-2026-123611 is a low-severity vulnerability in Rustls, classified under CWE-757. CVSS score: 3.7/10. Published 2026-11-08.
- How severe is CVE-2026-123611?
- Low severity. CVSS v3 base score is 3.7 out of 10.