Hostname deanonymization via outer ClientHello PSK disclosure
Published Jul 8, 2026 · Updated Jul 8, 2026
Information disclosure in Go crypto/tls allows attackers observing network traffic to identify hostnames protected by Encrypted Client Hello. clientHelloMsg.marshalMsg includes pre-shared key identities in the unencrypted outer ClientHello instead of omitting the PSK extension. The leak requires an ECH handshake carrying a pre-shared key identity; passive collection breaks hostname anonymity but does not alter the connection.
Summary
What happened
Information disclosure in Go crypto/tls allows attackers observing network traffic to identify hostnames protected by Encrypted Client Hello. clientHelloMsg.marshalMsg includes pre-shared key identities in the unencrypted outer ClientHello instead of omitting the PSK extension. The leak requires an ECH handshake carrying a pre-shared key identity; passive collection breaks hostname anonymity but does not alter the connection.
The record
- CVE
- CVE-2026-42505
- Published
- Jul 8, 2026
- Updated
- Jul 8, 2026
- Vendor
- Go standard library
- Product
- crypto/tls
- Classifications
- CWE-201, T1040
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 8, 2026CVE publishedPublication date reported by the CVE source.
- Jul 8, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <1.25.12
- Affected versionversion=1.26.0-0 <1.26.5
- Affected versionversion=1.27.0-0 <1.27.0-rc.2
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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