CVE-2026-44435: CWE-617: Reachable Assertion in h2o quicly
CVE-2026-44435 is a reachable assertion vulnerability in the quicly implementation of the IETF QUIC protocol used by the H2O HTTP server. The issue occurs when the total number of valid handshake messages received over a CRYPTO stream in a single packet number space exceeds 32KB, triggering an assertion failure and causing a denial of service. This vulnerability has been fixed by commit 937d0e9. The CVSS score is 7.5, indicating a high severity denial of service impact without confidentiality or integrity loss.
AI Analysis
Technical Summary
The vulnerability in quicly (part of the H2O HTTP server) is a reachable assertion failure triggered when the cumulative size of valid handshake messages on a CRYPTO stream for a single packet number space exceeds 32KB. This causes the application to crash, resulting in a denial of service condition. The issue was resolved by a specific code commit (937d0e9). There is no indication of confidentiality or integrity impact. No known exploits are reported in the wild. The vulnerability is tracked as CVE-2026-44435 with a CVSS v3.1 score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
Potential Impact
Successful exploitation causes a denial of service by crashing the affected service due to an assertion failure. There is no impact on confidentiality or integrity. The vulnerability affects availability only.
Mitigation Recommendations
A fix has been implemented in commit 937d0e9. Although no official patch or vendor advisory is provided in this data, the issue is resolved in the codebase at that commit. Users should update to the version including this commit to remediate the vulnerability. Patch status is not yet confirmed via a vendor advisory; check the official H2O or quicly repositories for the fixed version and apply updates accordingly.
CVE-2026-44435: CWE-617: Reachable Assertion in h2o quicly
Description
CVE-2026-44435 is a reachable assertion vulnerability in the quicly implementation of the IETF QUIC protocol used by the H2O HTTP server. The issue occurs when the total number of valid handshake messages received over a CRYPTO stream in a single packet number space exceeds 32KB, triggering an assertion failure and causing a denial of service. This vulnerability has been fixed by commit 937d0e9. The CVSS score is 7.5, indicating a high severity denial of service impact without confidentiality or integrity loss.
CVSS v3.1
Score 7.5high
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in quicly (part of the H2O HTTP server) is a reachable assertion failure triggered when the cumulative size of valid handshake messages on a CRYPTO stream for a single packet number space exceeds 32KB. This causes the application to crash, resulting in a denial of service condition. The issue was resolved by a specific code commit (937d0e9). There is no indication of confidentiality or integrity impact. No known exploits are reported in the wild. The vulnerability is tracked as CVE-2026-44435 with a CVSS v3.1 score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).
Potential Impact
Successful exploitation causes a denial of service by crashing the affected service due to an assertion failure. There is no impact on confidentiality or integrity. The vulnerability affects availability only.
Mitigation Recommendations
A fix has been implemented in commit 937d0e9. Although no official patch or vendor advisory is provided in this data, the issue is resolved in the codebase at that commit. Users should update to the version including this commit to remediate the vulnerability. Patch status is not yet confirmed via a vendor advisory; check the official H2O or quicly repositories for the fixed version and apply updates accordingly.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-05-06T14:40:00.954Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a59635868715ace43da39d2
Added to database: 07/16/2026, 23:03:52 UTC
Last enriched: 07/16/2026, 23:17:35 UTC
Last updated: 07/16/2026, 23:17:35 UTC
Views: 3
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