Quicly has assertion failures

published 2026-01-19 9 mo ago modified 2026-06-17 4 mo ago also EUVD-2025-206302

cvss: 7.5; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.4%; EPSS 0.4% chance of exploitation in 30 days, percentile 33%
public exploits: 0; none known

Quicly, an IETF QUIC protocol implementation, is susceptible to a denial-of-service attack prior to commit d9d3df6a8530a102b57d840e39b0311ce5c9e14e. A remote attacker can exploit these bugs to trigger an assertion failure that crashes process using Quicly. Commit d9d3df6a8530a102b57d840e39b0311ce5c9e14e fixes the issue.

Patch / fix

fixed in 1 links 1

h2o quicly 2026-01-18

github.com/h2o/quicly@d9d3df6 commit

CISA SSVC

Exploitation: none
Automatable: yes
Technical impact: partial
Assessed: 9 mo ago (2026-01-20)

Exploit prediction

0.40% chance of exploitation in the next 30 days, higher than 33% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	7.5	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected products

h2o quicly

Classification

Weakness

CWE-20 Improper Input Validation
CWE-617 Reachable Assertion

References

github.com /h2o/quicly/commit/d9d3df6a8530a102b57d840e39b0311ce5c9e14e
patch
github.com /h2o/quicly/security/advisories/GHSA-wr3c-345m-43v9
vendor-advisory

Sources

CVE List CVE-2025-61684
NVD CVE-2025-61684

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary