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Vulnerabilities

Vulnerability · GHSA-w44r-93j7-qv28

rustls: An unauthenticated ServerHello poisons the per-name key-exchange record, so later ClientHellos carry only a classical X25519 share

Published Oct 27, 2026 · catalog updated Oct 27, 2026 · rustls: An unauthenticated ServerHello

Last checked Oct 29, 2026. A connected source was read within the last 7 days.

Open the advisory

Exploitation likelihood is not on this record for GHSA-w44r-93j7-qv28. A missing EPSS score is not a low risk. Compare rustls: An unauthenticated ServerHello with the linked advisory before you change production.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (rustls: An unauthenticated ServerHello).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
  • EPSS is missing. A missing score is not a low risk.
Severity
Low3.7
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
Awaiting synchronization with FIRST
Remediation
Version ranges on file
Affected products
crates.io rustls · rust rustls

## Summary The client records the server-selected key-exchange group per server name when it processes the ServerHello, before the server is authenticated. A network attacker can answer one connection attempt for a target name with a ServerHello that selects X25519 and close the connection. Later ClientHellos for that name carry one X25519 share while supported_groups still lists X25519MLKEM768 first. If the server accepts that share instead of sending a HelloRetryRequest, the handshake completes with classical key exchange only and no error. An attacker that answers one connection attempt for the target name with a ServerHello selecting X25519 changes every later ClientHello of that client for that name, for as long as the entry stays in the store. No certificate or completed handshake is needed: it parses the ClientHello, sends the ServerHello, and closes. TLS 1.3 transcript binding stops an on-path attacker from editing the ClientHello of one connection. It does not stop the attacker from steering the client's prediction state beforehand, because that state is written from an unauthenticated message. ## What does not trigger it - Servers that send a HelloRetryRequest. The connection stays hybrid and costs one extra round trip. - A client configuration with resumption disabled: nothing is stored. - A different server name: the record is per name. ## Impact If the genuine server picks the group for which a share is present, instead of sending a HelloRetryRequest for its preferred hybrid group, the handshake completes with classical key exchange only, between two peers that both support the hybrid group. No error is raised. The confidentiality of recorded sessions against a future quantum adversary is lost for those connections (harvest now, decrypt later). There is no key compromise and no authentication bypass. Note that this behaviour is discussed at length in [draft-ietf-tls-key-share-prediction](https://www.ietf.org/archive/id/draft-ietf-tls-key-share-predictio

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • crates.io rustls0 → 0.23.46
  • crates.io rustls0.24.0-dev.1 → 0.24.0-dev.2
  • rust rustls< 0.23.46
  • rust rustls>= 0.24.0-dev.1, < 0.24.0-dev.2

How to fix GHSA-w44r-93j7-qv28

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

Exploitation likelihood is not on this record for GHSA-w44r-93j7-qv28. A missing EPSS score is not a low risk. Compare rustls: An unauthenticated ServerHello with the linked advisory before you change production.

Which versions are affected?

Compare what you have installed with 0 → 0.23.46, 0.24.0-dev.1 → 0.24.0-dev.2, < 0.23.46, >= 0.24.0-dev.1, < 0.24.0-dev.2. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-757. EPSS is not on this record yet. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 27, 2026 · GitHub Advisory Database

    Detected

    ## Summary The client records the server-selected key-exchange group per server name when it processes the ServerHello, before the server is authenticated. A network attacker can answer one connection attempt for a target name with a ServerHello that selects X25519 and close the connection. Later ClientHellos for that name carry one X25519 share while supported_groups still lists X25519MLKEM768 fi

  2. Oct 27, 2026 · GitHub Advisory Database

    Updated

    ## Summary The client records the server-selected key-exchange group per server name when it processes the ServerHello, before the server is authenticated. A network attacker can answer one connection attempt for a target name with a ServerHello that selects X25519 and close the connection. Later ClientHellos for that name carry one X25519 share while supported_groups still lists X25519MLKEM768 fi

  3. Oct 27, 2026 · GitHub Advisory Database

    Fix available

    rustls fixed in 0.23.46; rustls fixed in 0.24.0-dev.2

  4. Oct 27, 2026 · GitHub Advisory Database

    Fix available

    rustls fixed in 0.23.46

  5. Oct 27, 2026 · GitHub Advisory Database

    Fix available

    rustls fixed in 0.24.0-dev.2

  6. Oct 27, 2026 · GitHub Advisory Database

    Updated

    ## Summary The client records the server-selected key-exchange group per server name when it processes the ServerHello, before the server is authenticated. A network attacker can answer one connection attempt for a target name with a ServerHello that selects X25519 and close the connection. Later ClientHellos for that name carry one X25519 share while supported_groups still lists X25519MLKEM768 fi

Sources

References

Freshness

Last verified in this catalog Oct 27, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • GitHub Advisory DatabaseOct 29, 2026
  • OpenSSF OSV / OSV ScannerOct 29, 2026