CVE-2025-61684
CVE-2025-61684 is a high-severity vulnerability in H2o Quicly with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-617.
Key facts
- Severity: High (CVSS 3.x base score 7.5)
- EPSS exploit prediction: 0% (25th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2025-206302
- Weakness: CWE-617
- Affected product: H2o Quicly
- Published:
- Last modified:
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.
Frequently asked questions
- What is CVE-2025-61684?
- 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.
- How severe is CVE-2025-61684?
- CVE-2025-61684 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
- Is CVE-2025-61684 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (25th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2025-61684?
- CVE-2025-61684 affects H2o Quicly. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2025-61684?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
- Does CVE-2025-61684 have an EU (EUVD) identifier?
- Yes. CVE-2025-61684 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-206302.
- When was CVE-2025-61684 published?
- CVE-2025-61684 was published on 2026-01-19 and last updated on 2026-06-17.
References
- https://github.com/h2o/quicly/commit/d9d3df6a8530a102b57d840e39b0311ce5c9e14e
- https://github.com/h2o/quicly/security/advisories/GHSA-wr3c-345m-43v9
Affected products (1)
- cpe:2.3:a:h2o:quicly:*:*:*:*:*:*:*:*
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- CVE-2020-6619 — High (CVSS 8.8): stb stb_truetype.h through 1.22 has an assertion failure in stbtt__buf_seek.