High severity · published Jan 19, 2026
CVE-2025-61684
Quicly has assertion failures
7.5
CVSS
0.4%
EPSS
No
On KEV
Description
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 34% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
QU
quicly · h2o
< d9d3df6 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2025-61684
CVE.org
https://www.cve.org/CVERecord?id=CVE-2025-61684
Patch
https://github.com/h2o/quicly/commit/d9d3df6a8530a102b57d840e39b0311ce5c9e14e
Vendor Advisory
https://github.com/h2o/quicly/security/advisories/GHSA-wr3c-345m-43v9
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