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Fencer Intel
medium 5.3

CVE-2026-103399 json

Libsoup: soupserver: http/1 request smuggling via undrained expect: 100-continue body

published last mo. modified 4d ago also EUVD-2026-90226

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 15%
public exploits
0
none known

Summary

A flaw was found in SoupServer (libsoup). When an HTTP/1.x client sends a request with Expect: 100-continue and a request body, and SoupServer returns an early final (non-1xx) response before the body is read, the server neither drains the declared body bytes nor closes the connection. On a keep-alive connection, those leftover bytes are interpreted as a subsequent HTTP request. A remote, unauthenticated attacker can place a complete HTTP request in the body and cause SoupServer to process that smuggled request, leading to unintended request handling.

Patch / fix

  • libsoup3 Ubuntu 24.04 LTS 3.4.4-5ubuntu0.10
  • libsoup3 Ubuntu 26.10 3.6.6-1ubuntu3.1
  • libsoup3 Ubuntu 26.04 LTS 3.6.6-1ubuntu0.2
  • libsoup2.4 Ubuntu 22.04 LTS 2.74.2-3ubuntu0.10
  • libsoup2.4 Ubuntu 24.04 LTS 2.74.3-6ubuntu1.10
  • libsoup3 Ubuntu Pro 22.04 LTS 3.0.7-0ubuntu1+esm10
  • libsoup2.4 Ubuntu Pro 16.04 LTS 2.52.2-1ubuntu0.3+esm9
  • libsoup2.4 Ubuntu Pro 18.04 LTS 2.62.1-1ubuntu0.4+esm10

ubuntu advisories UBUNTU-CVE-2026-103399

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • libsoup SLES for SAP 15 SP5, SLES for SAP 15 SP4, SLES 15 SP5-LTSS +5 more 3.0.4-150400.3.58.1
  • libsoup SLES for SAP 15 SP6, SLES 15 SP6-LTSS, SLE Module for Basesystem 15 SP7 3.4.4-150600.3.62.1
  • libsoup SLES for SAP applications 16.0, SLES 16.0 3.6.6-160000.5.1
  • libsoup Linux Micro 6.0 3.4.2-159998.1.1
  • libsoup2 SLES for SAP 15 SP5, SLES for SAP 15 SP4, SLES 15 SP5-LTSS +8 more 2.74.3-150400.3.43.1
  • libsoup2 SLES for SAP 15 SP6, SLES 15 SP6-LTSS, SLE Module for Basesystem 15 SP7 2.74.3-150600.4.42.1
  • libsoup SLES LTSS Extended Security 12 SP5, SLES 12 SP5-LTSS 2.62.2-5.49.1

suse advisories SUSE-SU-2026:5063-1SUSE-SU-2026:5062-1SUSE-SU-2026:24470-1SUSE-SU-2026:24368-1SUSE-SU-2026:4739-1SUSE-SU-2026:4703-1

  • libsoup openSUSE Leap 16.0 3.6.6-160000.5.1
  • libsoup2 openSUSE Tumbleweed 2.74.3-25.1

opensuse advisories openSUSE-SU-2026:22181-1openSUSE-SU-2026:12132-1

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Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-103399 updated cvss 5.3

libsoup: SoupServer: HTTP/1 request smuggling via undrained Expect: 100-continue body

  • Red Hat Enterprise Linux 6 libsoup
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 7 libsoup Red Hat Enterprise Linux 8 libsoup Red Hat Enterprise Linux 9 libsoup Red Hat Enterprise Linux 10 libsoup3
    affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
last mo.

Exploit prediction

0.25% chance of exploitation in the next 30 days, higher than 15% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

Affected products

  • Red Hat Red Hat Enterprise Linux 10
  • Red Hat Red Hat Enterprise Linux 6
  • Red Hat Red Hat Enterprise Linux 7
  • Red Hat Red Hat Enterprise Linux 8
  • Red Hat Red Hat Enterprise Linux 9

Classification

Weakness
  • CWE-444 Inconsistent Interpretation of HTTP Requests

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.