CVE-2023-50247

h2o QUIC state exhaustion DoS

HIGH
7.5
CVSS Score
Published: December 12, 2023 at 07:56 PM UTC
Updated: June 17, 2026 at 06:39 AM UTC
2 products affected across 2 vendorsH2OH2O

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Severity
HIGH7.5
Exploit prediction
EPSS 0.9%

Description

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. The QUIC stack (quicly), as used by H2O up to commit 43f86e5 (in version 2.3.0-beta and prior), is susceptible to a state exhaustion attack. When H2O is serving HTTP/3, a remote attacker can exploit this vulnerability to progressively increase the memory retained by the QUIC stack. This can eventually cause H2O to abort due to memory exhaustion. The vulnerability has been resolved in commit d67e81d03be12a9d53dc8271af6530f40164cd35. HTTP/1 and HTTP/2 are not affected by this vulnerability as they do not use QUIC. Administrators looking to mitigate this issue without upgrading can disable HTTP/3 support.

Affected

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

v ≤ 2.3.0-beta2

Remediation

No guide yet

No remediation guidance has been written for this CVE yet. What the record does show:

CVSS

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

Quick Info

StatusMODIFIED
CWE
CWE-770

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