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CVE-2026-66338VulnerabilityPublished 07/24/2026Updated 10/17/2026

Libsoup2.4: A flaw was found in libsoup. The chunked transfer encoding parser uses a permissive parsing function for chunk sizes that silently accepts inputs… (CVE-2026-66338)

Affects libsoup2.4Source GCVE Database

0
CVSS 3.1 base score
7.2Medium
How severe the flaw is on the 0–10 CVSS scale.
Exploitation

Not in CISA KEV, no exploitation reported

EPSS
0.2% chance of exploitation in 30 days – higher than 20% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

What to do

Affected software

ProductAffectedFixed in
Ubuntu:Pro:16.04:LTSlibsoup2.4pkg:deb/ubuntu/libsoup2.4?arch=source&distro=esm-infra-legacy/xenialOther threatsAffected
  • =2.50.0-2debian1
  • =2.52.1-1
  • =2.52.2-1
  • =2.52.2-1ubuntu0.1
  • =2.52.2-1ubuntu0.2
  • =2.52.2-1ubuntu0.3
  • =2.52.2-1ubuntu0.3+esm1
  • =2.52.2-1ubuntu0.3+esm2
  • =2.52.2-1ubuntu0.3+esm3
  • =2.52.2-1ubuntu0.3+esm4
  • =2.52.2-1ubuntu0.3+esm5
  • =2.52.2-1ubuntu0.3+esm6
  • =2.52.2-1ubuntu0.3+esm7
  • =2.52.2-1ubuntu0.3+esm8
Fixed in–
Ubuntu:Pro:18.04:LTSlibsoup2.4pkg:deb/ubuntu/libsoup2.4?arch=source&distro=esm-infra/bionicOther threatsAffected
  • =2.60.1-1
  • =2.60.2-1
  • =2.60.2-2
  • =2.60.3-1
  • =2.61.90-1
  • =2.62.0-1
  • =2.62.1-1
  • =2.62.1-1ubuntu0.1
  • =2.62.1-1ubuntu0.3
  • =2.62.1-1ubuntu0.4
  • =2.62.1-1ubuntu0.4+esm1
  • =2.62.1-1ubuntu0.4+esm2
  • =2.62.1-1ubuntu0.4+esm3
  • =2.62.1-1ubuntu0.4+esm4
  • =2.62.1-1ubuntu0.4+esm5
  • =2.62.1-1ubuntu0.4+esm6
  • =2.62.1-1ubuntu0.4+esm7
  • =2.62.1-1ubuntu0.4+esm8
  • =2.62.1-1ubuntu0.4+esm9
Fixed in–
Ubuntu:Pro:20.04:LTSlibsoup2.4pkg:deb/ubuntu/libsoup2.4?arch=source&distro=esm-infra/focalOther threatsAffected
  • =2.68.2-0ubuntu1
  • =2.68.2-1
  • =2.68.2-2
  • =2.68.2-2build2
  • =2.69.90-1
  • =2.70.0-1
  • =2.70.0-1ubuntu0.1
  • =2.70.0-1ubuntu0.2
  • =2.70.0-1ubuntu0.3
  • =2.70.0-1ubuntu0.4
  • =2.70.0-1ubuntu0.5
  • =2.70.0-1ubuntu0.5+esm1
  • =2.70.0-1ubuntu0.5+esm2
  • =2.70.0-1ubuntu0.5+esm3
  • =2.70.0-1ubuntu0.5+esm4
Fixed in–
Ubuntu:22.04:LTSlibsoup2.4pkg:deb/ubuntu/libsoup2.4?arch=source&distro=jammyOther threatsAffected
  • =2.72.0-3ubuntu3
  • =2.74.1-1
  • =2.74.2-2
  • =2.74.2-3
  • =2.74.2-3ubuntu0.1
  • =2.74.2-3ubuntu0.2
  • =2.74.2-3ubuntu0.3
  • =2.74.2-3ubuntu0.4
  • =2.74.2-3ubuntu0.5
  • =2.74.2-3ubuntu0.6
  • =2.74.2-3ubuntu0.7
  • =2.74.2-3ubuntu0.8
  • =2.74.2-3ubuntu0.9
Fixed in–
Ubuntu:Pro:22.04:LTSlibsoup3pkg:deb/ubuntu/libsoup3?arch=source&distro=esm-apps/jammyOther threatsAffected
  • =3.0.4-2
  • =3.0.4-3
  • =3.0.5-1
  • =3.0.7-0ubuntu1
  • =3.0.7-0ubuntu1+esm1
  • =3.0.7-0ubuntu1+esm2
  • =3.0.7-0ubuntu1+esm3
  • =3.0.7-0ubuntu1+esm4
  • =3.0.7-0ubuntu1+esm5
  • =3.0.7-0ubuntu1+esm6
  • =3.0.7-0ubuntu1+esm7
  • =3.0.7-0ubuntu1+esm8
  • =3.0.7-0ubuntu1+esm9
Fixed in–
Ubuntu:24.04:LTSlibsoup2.4pkg:deb/ubuntu/libsoup2.4?arch=source&distro=nobleOther threatsAffected
  • =2.74.3-1
  • =2.74.3-2
  • =2.74.3-3
  • =2.74.3-6
  • =2.74.3-6build1
  • =2.74.3-6ubuntu1
  • =2.74.3-6ubuntu1.1
  • =2.74.3-6ubuntu1.2
  • =2.74.3-6ubuntu1.3
  • =2.74.3-6ubuntu1.4
  • =2.74.3-6ubuntu1.5
  • =2.74.3-6ubuntu1.6
  • =2.74.3-6ubuntu1.7
  • =2.74.3-6ubuntu1.8
  • =2.74.3-6ubuntu1.9
Fixed in–
Ubuntu:24.04:LTSlibsoup3pkg:deb/ubuntu/libsoup3?arch=source&distro=nobleOther threatsAffected
  • =3.4.2-4
  • =3.4.4-1
  • =3.4.4-2
  • =3.4.4-4
  • =3.4.4-5
  • =3.4.4-5build1
  • =3.4.4-5build2
  • =3.4.4-5ubuntu0.1
  • =3.4.4-5ubuntu0.2
  • =3.4.4-5ubuntu0.3
  • =3.4.4-5ubuntu0.4
  • =3.4.4-5ubuntu0.5
  • =3.4.4-5ubuntu0.6
  • =3.4.4-5ubuntu0.7
  • =3.4.4-5ubuntu0.8
  • =3.4.4-5ubuntu0.9
Fixed in–
Ubuntu:26.10libsoup2.4pkg:deb/ubuntu/libsoup2.4?arch=source&distro=stonkingOther threatsAffected
  • =2.74.3-10.1ubuntu5
Fixed in–
Ubuntu:26.10libsoup3pkg:deb/ubuntu/libsoup3?arch=source&distro=stonkingOther threatsAffected
  • =3.6.6-1
Fixed in–
Ubuntu:26.04:LTSlibsoup3pkg:deb/ubuntu/libsoup3?arch=source&distro=resoluteOther threatsAffected
  • =3.6.5-4
  • =3.6.5-5
  • =3.6.5-6
  • =3.6.5-7
  • =3.6.5-9
  • =3.6.6-1
  • =3.6.6-1ubuntu0.1
Fixed in–
Ubuntu:Pro:26.04:LTSlibsoup2.4pkg:deb/ubuntu/libsoup2.4?arch=source&distro=esm-apps/resoluteOther threatsAffected
  • =2.74.3-10.1ubuntu4
  • =2.74.3-10.1ubuntu5
  • =2.74.3-10.1ubuntu5+esm1
  • =2.74.3-10.1ubuntu5+esm2
  • =2.74.3-10.1ubuntu5+esm3
Fixed in–

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AI-suggested

Given the limited practical impact, immediate urgent action may not be necessary unless libsoup is deployed in a vulnerable configuration behind strict proxies.

Description

A vulnerability in libsoup's chunked transfer encoding parser allows permissive parsing of chunk sizes that violate RFC 9112. This flaw can lead to HTTP request smuggling when libsoup is used behind a strict frontend proxy. The parser accepts chunk sizes with leading whitespace, plus sign prefixes, and trailing invalid characters. The practical impact is limited because libsoup servers are rarely deployed in internet-facing roles behind reverse proxies. The vulnerability has a CVSS score of 7.2, indicating a medium severity level.

Impact

The vulnerability can lead to HTTP request smuggling attacks when libsoup is used behind a strict frontend proxy. This could allow an attacker to bypass security controls or interfere with HTTP request processing. However, the practical impact is limited because libsoup servers are rarely deployed in internet-facing roles behind reverse proxies. No known exploits in the wild have been reported.

Summary

The libsoup2.4 library contains a vulnerability in its chunked transfer encoding parser where the parser uses a permissive function to parse chunk sizes. This function accepts inputs that violate RFC 9112, including chunk sizes with leading whitespace, plus signs, and trailing invalid characters. This behavior can enable HTTP request smuggling attacks if libsoup is deployed behind a strict frontend proxy that enforces stricter parsing rules. The vulnerability affects multiple specific versions of libsoup2.4 as listed, but the practical impact is limited due to typical deployment scenarios. There is no explicit patch or remediation information provided in the input data.

Weaknesses

References

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