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Vulnerability · Published Sep 30, 2026 · Assigned by redhat

CVE-2026-103399Libsoup: soupserver: http/1 request smuggling via undrained expect: 100-continue body

Medium 5.3

In plain English

A medium-severity security flaw in Red Hat Enterprise Linux 10 from Red Hat. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 16% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)5.3Medium
Exploit odds (30 days)0.2%top 84.1% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Debian:12libsoup2.4no fix listedDEBIAN-CVE-2026-103399
Debian:13libsoup2.4no fix listedDEBIAN-CVE-2026-103399
Debian:12libsoup3no fix listedDEBIAN-CVE-2026-103399
Debian:13libsoup3no fix listedDEBIAN-CVE-2026-103399
Ubuntu:22.04:LTSlibsoup2.42.74.2-3ubuntu0.10USN-8975-1
Ubuntu:22.04:LTSlibsoup2.42.74.2-3ubuntu0.10UBUNTU-CVE-2026-103399
Ubuntu:24.04:LTSlibsoup2.42.74.3-6ubuntu1.10USN-8975-1
Ubuntu:24.04:LTSlibsoup2.42.74.3-6ubuntu1.10UBUNTU-CVE-2026-103399
Ubuntu:26.10libsoup2.4no fix listedUBUNTU-CVE-2026-103399
Ubuntu:24.04:LTSlibsoup33.4.4-5ubuntu0.10UBUNTU-CVE-2026-103399
Ubuntu:24.04:LTSlibsoup33.4.4-5ubuntu0.10USN-8975-1
Ubuntu:26.04:LTSlibsoup33.6.6-1ubuntu0.2USN-8975-1
Ubuntu:26.04:LTSlibsoup33.6.6-1ubuntu0.2UBUNTU-CVE-2026-103399
Ubuntu:26.10libsoup33.6.6-1ubuntu3.1UBUNTU-CVE-2026-103399
Ubuntu:26.10libsoup33.6.6-1ubuntu3.1USN-8975-1

Affected products (as reported)

VendorProductVersions
Red Hat Red Hat Enterprise Linux 10 see references
Red Hat Red Hat Enterprise Linux 6 see references
Red Hat Red Hat Enterprise Linux 7 see references
Red Hat Red Hat Enterprise Linux 8 see references
Red Hat Red Hat Enterprise Linux 9 see references

Weakness: CWE-444 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N

References