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TI-2026-86753 Aliases CVE-2026-123611GHSA-jh53-vxwq-v4wp

Key exchange downgrade in rustls via unauthenticated ServerHello

Priority MEDIUM 43CWE-757Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
High
Attack requirements
Present
Impact type
—
Confidentiality · integrity · availability
Low · None · None
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA.

Summary

rustls before 0.23.46 contains a key exchange downgrade flaw in how it records the key exchange group per server name. A network attacker can answer one connection with an unauthenticated ServerHello that selects X25519, so later ClientHellos send only classical key shares and lose post-quantum confidentiality. The weakness is CWE-757, selection of a less-secure algorithm during negotiation.

Written with Claude Haiku 5.5 from the sources below · 2026-11-08

Description from the CNA

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.

Why it matters now

Fix Fixed rustls (rustls): 0.23.46

SSVC decision points

Not available: CISA has not published SSVC decision points for this record.

Affected products

VendorProductAffected versionsFixed inStatusSource
rustlsrustlsbefore 0.23.460.23.46Patch availableCNA
  • rustls Vendorrustls Affected before 0.23.46 Fixed in 0.23.46 Patch available CNA

Remediation

Update rustls to version 0.23.46 or later.

Written with Claude Haiku 5.5 from the sources below · 2026-11-08

  • Fix · CNA rustls (rustls) Fixed in 0.23.46

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

  • Release ·

    rustls 0.23.46

    3 records Highest priority Priority MEDIUM 2 MEDIUM, 1 LOW

    Other records, highest priority first

    • TI-2026-86752 Uncontrolled memory allocation in rustls Brotli certificate decompressionPriority MEDIUM 43
    • TI-2026-86754 Application data sent to public_name server when rustls rejects ECHPriority LOW 36
    Show all 3 records →

Timeline

  1. 2026-11-08 Threatist record created from CVE-2026-123611
  2. 2026-11-08 Alias added: GHSA-jh53-vxwq-v4wp

References

Advisory 1

  • TI-2026-63063 rustls-webpki before 0.103.13 Panic via empty BIT STRING CVSS 4.0HIGH 8.7
  • TI-2026-86755 Rustls accepts handshake messages at the wrong encryption level CVSS 4.0MEDIUM 6.9
  • TI-2026-86752 Uncontrolled memory allocation in rustls Brotli certificate decompression CVSS 4.0MEDIUM 6.3
  • TI-2024-21532 Rustls vulnerable to an infinite loop in rustls::conn::ConnectionCommon::complete_io() with proper client input CVSS 3.1HIGH 7.5
  • TI-2026-86754 Application data sent to public_name server when rustls rejects ECH CVSS 4.0MEDIUM 4.6
  • TI-2026-86751 Secret key material exposed through Debug formatting in Rustls CVSS 4.0MEDIUM 4.1
See all 9 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences