CVE-2024-45403

H2O assertion failure when HTTP/3 requests are cancelled

HIGH
7.5
CVSS Score
Published: October 11, 2024 at 02:28 PM UTC
Updated: June 17, 2026 at 07:54 AM UTC
2 products affected across 2 vendorsH2OH2O

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Severity
HIGH7.5
Exploit prediction
EPSS 0.7%
SSVC
No known exploit

Description

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. When h2o is configured as a reverse proxy and HTTP/3 requests are cancelled by the client, h2o might crash due to an assertion failure. The crash can be exploited by an attacker to mount a Denial-of-Service attack. By default, the h2o standalone server automatically restarts, minimizing the impact. However, HTTP requests that were served concurrently will still be disrupted. The vulnerability has been addressed in commit 1ed32b2. Users may disable the use of HTTP/3 to mitigate the issue.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

2024-06-18 ≤ v < 2024-09-04
Affected range stops below 2024-09-04, so it looks safe — our inference, not a vendor statement
v < 1ed32b23f999acf0c5029f09c8525f93eb1d354c

SSVC — Action Prioritization

SSVCNo known exploitNot automatablePartial impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
Vector?

Quick Info

StatusANALYZED
CWE
CWE-617

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