CVE-2023-50247: h2o QUIC state exhaustion DoS
Vulnerability summary
CVE-2023-50247 is a high (CVSS 7.5) vulnerability in dena h2o. EPSS estimates a 0.86% chance of exploitation in the next 30 days, higher than 58.4% of scored vulnerabilities.
Not severe (CVSS 3.7, network access); no exploitation reported by the 5 checked sources
Source freshness unavailable
How is this decided?Timeline
- 12-12-2023PublishedVulnerability first disclosed.
- 02-08-2024Last modifiedVulnerability information updated.
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.
CVSS metrics
2 scores · 2 sources · 1 version- CVE.orgCNA3.7LowCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:LDiffers
EPSS trend
Probability
0.86%
Chance of exploitation in the next 30 days
Percentile
58%
Versus all other CVEs
30-day change
No change 0.00 pp
From 0.86% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.
Dena1 product
- h2o≤ 2.2.6 | 2.3.0:beta1 | 2.3.0:beta2
H2o1 product
- h2o≤ 2.3.0-beta2
2 vendors · 2 products