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CVE-2021-43848

Published: 1 February 2022

h2o is an open source http server. In code prior to the `8c0eca3` commit h2o may attempt to access uninitialized memory. When receiving QUIC frames in certain order, HTTP/3 server-side implementation of h2o can be misguided to treat uninitialized memory as HTTP/3 frames that have been received. When h2o is used as a reverse proxy, an attacker can abuse this vulnerability to send internal state of h2o to backend servers controlled by the attacker or third party. Also, if there is an HTTP endpoint that reflects the traffic sent from the client, an attacker can use that reflector to obtain internal state of h2o. This internal state includes traffic of other connections in unencrypted form and TLS session tickets. This vulnerability exists in h2o server with HTTP/3 support, between commit 93af138 and d1f0f65. None of the released versions of h2o are affected by this vulnerability. There are no known workarounds. Users of unreleased versions of h2o using HTTP/3 are advised to upgrade immediately.

Priority

Medium

Cvss 3 Severity Score

5.9

Score breakdown

Status

Package Release Status
h2o
Launchpad, Ubuntu, Debian
bionic Needs triage

focal Needs triage

impish Ignored
(end of life)
trusty Ignored
(end of standard support)
upstream Needs triage

xenial Ignored
(end of standard support)
kinetic Ignored
(end of life, was needs-triage)
jammy Needs triage

mantic Needs triage

lunar Ignored
(end of life, was needs-triage)

Severity score breakdown

Parameter Value
Base score 5.9
Attack vector Network
Attack complexity High
Privileges required None
User interaction None
Scope Unchanged
Confidentiality High
Integrity impact None
Availability impact None
Vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N