Group-policy bypass via unchecked HelloRetryRequest selection
Published Sep 14, 2026 · Updated Sep 14, 2026
TLS 1.3 group-policy bypass in Mbed TLS 3.5.0 through 3.6.6 and 4.0.0 through 4.1.1 allows remote attackers to select unadvertised groups. The TLS 1.3 client HelloRetryRequest handler fails to verify that selected_group appeared in the original ClientHello supported_groups extension. Exposure requires TLS 1.3 ephemeral or PSK-ephemeral exchange, an application-enforced group restriction, and connection to a malicious server; the bypass can violate cryptographic policy or abort the handshake but does not expose keys or certificates.
Summary
What happened
TLS 1.3 group-policy bypass in Mbed TLS 3.5.0 through 3.6.6 and 4.0.0 through 4.1.1 allows remote attackers to select unadvertised groups. The TLS 1.3 client HelloRetryRequest handler fails to verify that selected_group appeared in the original ClientHello supported_groups extension. Exposure requires TLS 1.3 ephemeral or PSK-ephemeral exchange, an application-enforced group restriction, and connection to a malicious server; the bypass can violate cryptographic policy or abort the handshake but does not expose keys or certificates.
The record
- CVE
- CVE-2026-25832
- Published
- Sep 14, 2026
- Updated
- Sep 14, 2026
- Vendor
- TrustedFirmware.org
- Product
- Mbed TLS
- Classifications
- Unavailable
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 14, 2026CVE publishedPublication date reported by the CVE source.
- Sep 14, 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=3.5.0 <3.6.7
- Affected versionversion=4.0.0 <4.1.2
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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Weakness, pattern, technique
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Public exploit references
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Technologies
Your stack
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Your stack
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