Port-blocking bypass via unchecked Alt-Svc integer
Published Jun 24, 2021 · Updated Aug 3, 2024
Port-blocking bypass in Firefox before 88, Firefox ESR before 78.10, and Thunderbird before 78.10 allows remote attackers to reach blocked ports. nsHttpChannel::ProcessAltService passes an Alt-Svc port to AltSvcMapping::ProcessHeader, which parses it as int32_t without enforcing the 16-bit port range before AllowPort checks blocked ports. A user must load attacker-controlled web content that returns a crafted Alt-Svc header; the bypass redirects client traffic to services on otherwise prohibited ports.
Summary
What happened
Port-blocking bypass in Firefox before 88, Firefox ESR before 78.10, and Thunderbird before 78.10 allows remote attackers to reach blocked ports. nsHttpChannel::ProcessAltService passes an Alt-Svc port to AltSvcMapping::ProcessHeader, which parses it as int32_t without enforcing the 16-bit port range before AllowPort checks blocked ports. A user must load attacker-controlled web content that returns a crafted Alt-Svc header; the bypass redirects client traffic to services on otherwise prohibited ports.
The record
- CVE
- CVE-2021-29946
- Published
- Jun 24, 2021
- Updated
- Aug 3, 2024
- Vendor
- Mozilla
- Product
- Firefox
- Classifications
- CWE-190, T1189
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 24, 2021CVE publishedPublication date reported by the CVE source.
- Aug 3, 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?
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- Affected versionversion=unspecified <88
What conditions does exploitation require?
What is affected?
Published CVSS scores
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Attacks
What attackers are doing with it
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Public exploit references
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Technologies
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Your stack
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