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Vulnerability record · CVE-2026-103399 · published 30 September 2026

CVE-2026-103399: HTTP request smuggling vulnerability

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.

5.3 CVSS 3.1 Medium CWE-444 · HTTP request smuggling Awaiting Analysis
5.3CVSS 3.1 base score
-EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
2References
30 Sep 2026Last modified by NVD

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.

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

References

LinkTags
https://access.redhat.com/security/cve/CVE-2026-103399
https://bugzilla.redhat.com/show_bug.cgi?id=2543949

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Source: NIST National Vulnerability Database (record CVE-2026-103399), CISA KEV, FIRST EPSS. This page is refreshed as NVD updates the record.