Cross-port TLS content disclosure via cached opt-in
Published Dec 8, 2021 · Updated Aug 4, 2024
Origin validation error in Firefox before 94 and Firefox ESR and Thunderbird before 91.3 allows remote attackers to read cross-port TLS content. The HTTP/2 Opportunistic Encryption implementation checks a .well-known opt-in only on the first alternative-service connection, then reuses that result for later TLS ports. Exploitation requires user navigation plus an active network attacker able to manipulate DNS and forward connections, exposing content served by another encrypted port.
Summary
What happened
Origin validation error in Firefox before 94 and Firefox ESR and Thunderbird before 91.3 allows remote attackers to read cross-port TLS content. The HTTP/2 Opportunistic Encryption implementation checks a .well-known opt-in only on the first alternative-service connection, then reuses that result for later TLS ports. Exploitation requires user navigation plus an active network attacker able to manipulate DNS and forward connections, exposing content served by another encrypted port.
The record
- CVE
- CVE-2021-38507
- Published
- Dec 8, 2021
- Updated
- Aug 4, 2024
- Vendor
- Mozilla
- Product
- Firefox
- Classifications
- CWE-346, T1557
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Dec 8, 2021CVE publishedPublication date reported by the CVE source.
- Aug 4, 2024Record 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=unspecified <94
What conditions does exploitation require?
What is affected?
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.
Public exploit references
- Mozilla Bugzilla reproduction stepsproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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