CVE-2026-66338

Publication date 24 July 2026

Last updated 30 September 2026

Ubuntu priority

Cvss 3 Severity Score

Description

A flaw was found in libsoup. The chunked transfer encoding parser uses a permissive parsing function for chunk sizes that silently accepts inputs violating RFC 9112, including leading whitespace, plus sign prefixes, and trailing invalid characters. When libsoup operates behind a strict frontend proxy, this parsing differential can be exploited to smuggle HTTP requests.

Status

Show unmaintained releases

Package	Ubuntu Release	Status
libsoup2.4	26.04 LTS resolute	Vulnerable, fix deferred
	24.04 LTS noble	Vulnerable, fix deferred
	22.04 LTS jammy	Vulnerable, fix deferred
	20.04 LTS focal	Vulnerable, fix deferred
	18.04 LTS bionic	Vulnerable, fix deferred
	16.04 LTS xenial	Vulnerable, fix deferred
libsoup3	26.04 LTS resolute	Vulnerable, fix deferred
	24.04 LTS noble	Vulnerable, fix deferred
	22.04 LTS jammy	Vulnerable, fix deferred

Patch details

For informational purposes only. We recommend not to cherry-pick updates. How can I get the fixes?

Package	Patch details
libsoup2.4	Upstream: 96ac392
libsoup3	Upstream: 96ac392

Severity score breakdown

CVSS version: CVSS v3.0

Base score 5.4 · Medium

Base metrics

Parameter	Value
Attack vector	Network
Attack complexity	High
Privileges required	None
User interaction	None
Scope	Changed
Confidentiality impact	Low
Integrity impact	Low
Availability impact	None

Scores

Parameter	Value
Base score	5.4 · Medium
Exploitability score	-
Impact score	-

Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:L/I:L/A:N