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Libsoup2.4: A flaw was found in SoupServer (libsoup). (CVE-2026-103399)

0
Medium
VulnerabilityCVE-2026-103399gcveosvubuntu-cve-2026-103399cve-2026-103399ubuntu-pro-16-04-ltsubuntu-pro-18-04-ltsubuntu-pro-20-04-ltsubuntu-22-04-ltsubuntu-pro-22-04-ltsubuntu-24-04-ltsubuntu-26-10ubuntu-26-04-ltsubuntu-pro-26-04-lts
Published: 09/30/2026 (09/30/2026, 18:18:00 UTC)
Source: GCVE Database
Product: libsoup2.4

Description

A vulnerability in libsoup2.4's SoupServer allows an unauthenticated remote attacker to perform HTTP request smuggling. When an HTTP/1.x client sends a request with 'Expect: 100-continue' and a request body, if SoupServer returns a final response before reading the body, it neither drains the body nor closes the connection. This causes leftover bytes to be interpreted as a new HTTP request, potentially leading to unintended request handling. The issue affects many specific versions of libsoup2.4. The CVSS score is 5.3, indicating a medium severity level.

CVSS v3.1

Score 5.3medium

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected software

Ubuntu:Pro:16.04:LTSmore threats →ghsa
libsoup2.4
pkg:deb/ubuntu/libsoup2.4?arch=source&distro=esm-infra-legacy/xenial
Affected versions
=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
Ubuntu:Pro:18.04:LTSmore threats →ghsa
libsoup2.4
pkg:deb/ubuntu/libsoup2.4?arch=source&distro=esm-infra/bionic
Affected versions
=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
Ubuntu:Pro:20.04:LTSmore threats →ghsa
libsoup2.4
pkg:deb/ubuntu/libsoup2.4?arch=source&distro=esm-infra/focal
Affected versions
=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
Ubuntu:22.04:LTSmore threats →ghsa
libsoup2.4
pkg:deb/ubuntu/libsoup2.4?arch=source&distro=jammy
Affected versions
=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
Ubuntu:Pro:22.04:LTSmore threats →ghsa
libsoup3
pkg:deb/ubuntu/libsoup3?arch=source&distro=esm-apps/jammy
Affected versions
=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
Ubuntu:24.04:LTSmore threats →ghsa
libsoup2.4
pkg:deb/ubuntu/libsoup2.4?arch=source&distro=noble
Affected versions
=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
Ubuntu:24.04:LTSmore threats →ghsa
libsoup3
pkg:deb/ubuntu/libsoup3?arch=source&distro=noble
Affected versions
=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
Ubuntu:26.10more threats →ghsa
libsoup2.4
pkg:deb/ubuntu/libsoup2.4?arch=source&distro=stonking
Affected versions
=2.74.3-10.1ubuntu5
Ubuntu:26.10more threats →ghsa
libsoup3
pkg:deb/ubuntu/libsoup3?arch=source&distro=stonking
Affected versions
=3.6.6-1
Ubuntu:26.04:LTSmore threats →ghsa
libsoup3
pkg:deb/ubuntu/libsoup3?arch=source&distro=resolute
Affected versions
=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
Ubuntu:Pro:26.04:LTSmore threats →ghsa
libsoup2.4
pkg:deb/ubuntu/libsoup2.4?arch=source&distro=esm-apps/resolute
Affected versions
=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

Run on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.

AI-Powered Analysis

Machine-generated threat intelligence

AILast updated: 10/17/2026, 22:43:33 UTC

Technical Analysis

CVE-2026-103399 describes a flaw in libsoup2.4's SoupServer component where, upon receiving an HTTP/1.x request with 'Expect: 100-continue' and a request body, if the server sends an early final (non-1xx) response before reading the body, it fails to drain the declared body bytes or close the connection. On persistent (keep-alive) connections, the leftover bytes are interpreted as a subsequent HTTP request, allowing a remote unauthenticated attacker to smuggle a complete HTTP request within the body. This can cause the server to process unintended requests, potentially leading to unexpected behavior or request handling.

Potential Impact

The vulnerability allows a remote unauthenticated attacker to smuggle HTTP requests by embedding a complete HTTP request in the body of an initial request. This can cause the server to process unintended requests, which may lead to unintended request handling. There is no direct confidentiality or availability impact indicated, but the integrity of request handling is affected.

Mitigation Recommendations

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a patch is available, consider disabling HTTP/1.x keep-alive connections or the handling of 'Expect: 100-continue' headers if feasible, to mitigate the risk of request smuggling. Monitor vendor communications for official fixes.

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Technical Details

Gcve Source
db.gcve.eu
Osv Id
UBUNTU-CVE-2026-103399
Osv Schema Version
1.7.0
Ecosystems
["Ubuntu:Pro:16.04:LTS","Ubuntu:Pro:18.04:LTS","Ubuntu:Pro:20.04:LTS","Ubuntu:22.04:LTS","Ubuntu:Pro:22.04:LTS","Ubuntu:24.04:LTS","Ubuntu:26.10","Ubuntu:26.04:LTS","Ubuntu:Pro:26.04:LTS"]
Cvss Version
3.1
State
PUBLISHED

Threat ID: 6ad3f4f62cdf04f656657605

Added to database: 10/17/2026, 22:21:42 UTC

Last enriched: 10/17/2026, 22:43:33 UTC

Last updated: 10/17/2026, 22:43:33 UTC

Views: 2

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