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Vulnerability record · CVE-2026-66338 · published 24 July 2026

CVE-2026-66338: Gnome libsoup http request smuggling vulnerability

Gnome · Libsoup

A flaw was found in libsoup. The chunked transfer encoding parser uses a permissive parsing function for chunk sizes that silently accepts inputs violating RFC 9112, including leading whitespace, plus sign prefixes, and trailing invalid characters. When libsoup operates behind a strict frontend proxy, this parsing differential can be exploited to smuggle HTTP requests.

7.2 CVSS 3.1 High EPSS 0.28% · top 81.9% CWE-444 · HTTP request smuggling
7.2CVSS 3.1 base score
0.28%EPSS exploitation probability, 30 days
NoNot in CISA KEV
2Affected product versions listed by NVD
2References, 1 tagged exploit
24 Aug 2026Last modified by NVD

Description

A flaw was found in libsoup. The chunked transfer encoding parser uses a permissive parsing function for chunk sizes that silently accepts inputs violating RFC 9112, including leading whitespace, plus sign prefixes, and trailing invalid characters. When libsoup operates behind a strict frontend proxy, this parsing differential can be exploited to smuggle HTTP requests.

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

Affected products

2 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://access.redhat.com/security/cve/CVE-2026-66338 Vendor Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2506950 ExploitIssue TrackingVendor Advisory

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-66338), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.