CVE-2026-55368
HIGH
MEDIUM
Priority: 0.03
BB Relevance:
66/100
Published: 2026-11-04
Modified: 2026-11-12
First seen: 2026-11-04
Status: active
Attack Surface
Network
No Auth
No Interaction
Conf. Impact
Integ. Impact
CVSS Vector Breakdown
AV:
Network
AC:
High
PR:
None
UI:
None
S:
Unchanged
C:
High
I:
High
A:
High
Description
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 48b7ae12107fd2b118e4641da49599e9aac8edd8, H2O's access-log formatter could write past its log-line buffer when an affected custom access-log format was configured. The allocation errors affected %{error}x, %q when the query string was empty, and numeric elements whose temporary terminating NUL reached the end of the buffer. A matching request could crash the server, while the effect of the one-byte NUL overwrite beyond a crash was not established. This vulnerability is fixed with commit 48b7ae12107fd2b118e4641da49599e9aac8edd8.
Weakness Classification (1)
Affected Software (2)
References & Advisories (3)
x_refsource_MISC
x_refsource_MISC
x_refsource_CONFIRM