CVE-2026-44434 (CVSS 5.3)

Description

Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server. Prior to commit dccf5d4, Quicly was vulnerable to stateless reset injection through lack of packet entry validation. The QUIC protocol is designed to withstand packet injection attacks, once the handshake is complete. Only packets that carry some secret patterns are considered as stateless resets. Quicly allows the peer to share up to 4 such patterns per connection. However, until now, it failed to determine which of the 4 slots that it uses to retain the secret patterns contains a valid entry. As the slots are zero-initialized, the failure meant that, unless the peer advertised 4 of such patterns, an all-zero pattern was treated as a stateless reset.In effect, this allowed an on-path attacker to reset QUIC connections governed by Quicly. This issue has been fixed by commit dccf5d4.

Is your site exposed to CVE-2026-44434?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

5.3

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS — Exploit Prediction

0.0015

Probability of exploitation

0.04%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-345 CWE-345

CWE-665 CWE-665

References

Other References

https://github.com/h2o/quicly/commit/dccf5d4579c7ae9dd6e8f90c36d52e311bb60710 https://github.com/h2o/quicly/security/advisories/GHSA-899f-49jq-pfh8

Frequently Asked Questions

What is CVE-2026-44434? +

Quicly is an IETF QUIC protocol implementation intended primarily for use within the H2O HTTP server. Prior to commit dccf5d4, Quicly was vulnerable to stateless reset injection through lack of packet entry validation. The QUIC protocol is designed to withstand packet injection attacks, once the handshake is complete. Only packets that carry some secret patterns are considered as stateless resets. Quicly allows the peer to share up to 4 such patterns per connection. However, until now, it failed to determine which of the 4 slots that it uses to retain the secret patterns contains a valid entry. As the slots are zero-initialized, the failure meant that, unless the peer advertised 4 of such patterns, an all-zero pattern was treated as a stateless reset.In effect, this allowed an on-path attacker to reset QUIC connections governed by Quicly. This issue has been fixed by commit dccf5d4. It has a CVSS v3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2026-44434? +

CVE-2026-44434 has a CVSS v3.1 score of 5.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0015, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-44434? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2026-45022

go-git is an extensible git implementation library written in pure Go. Prior to 5.19.0 and 6.0.0-alpha.3, go-git may parse malformed …

CVE-2026-42206

Roadiz is a polymorphic content management system based on a node system. Prior to versions 2.3.43, 2.5.45, 2.6.31, and 2.7.18, …

CVE-2026-47202

Kavita is a cross platform reading server. Prior to 0.9.0.2, an Improper Token validation flaw permits a remote and unauthenticated …

CVE-2025-21606

stats is a macOS system monitor in for the menu bar. The Stats application is vulnerable to a local privilege …

CVE-2025-25188

Hickory DNS is a Rust based DNS client, server, and resolver. A vulnerability present starting in version 0.8.0 and prior …

CVE-2025-52484

RISC Zero is a general computing platform based on zk-STARKs and the RISC-V microarchitecture. Due to a missing constraint in …

CVE-2026-44434