Connection interruption via zero-initialized reset tokens
Published Jul 16, 2026 · Updated Jul 16, 2026
Stateless reset injection in H2O quicly before commit dccf5d4 allows man-in-the-middle attackers to interrupt established QUIC connections. The is_stateless_reset function checks every connection-ID slot but tests slot zero's state on every iteration, leaving unused zero-initialized slots eligible so an all-zero packet suffix matches their reset token. An attacker positioned on the network path after the handshake can forge such a packet to terminate the connection without reading or altering application data.
Summary
What happened
Stateless reset injection in H2O quicly before commit dccf5d4 allows man-in-the-middle attackers to interrupt established QUIC connections. The is_stateless_reset function checks every connection-ID slot but tests slot zero's state on every iteration, leaving unused zero-initialized slots eligible so an all-zero packet suffix matches their reset token. An attacker positioned on the network path after the handshake can forge such a packet to terminate the connection without reading or altering application data.
The record
- CVE
- CVE-2026-44434
- Published
- Jul 16, 2026
- Updated
- Jul 16, 2026
- Vendor
- H2O Project
- Product
- quicly
- Classifications
- CWE-345, CWE-665, T1499
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 16, 2026CVE publishedPublication date reported by the CVE source.
- Jul 16, 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?
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- Affected versionversion=< dccf5d4
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
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Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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