What’s Vulnerable › Vulnerabilities

CVE-2026-66338: Libsoup: libsoup: http request smuggling via permissive chunk-size parsing in soup_body_input_stream_read_chunked()

• Severity: high (CVSS 7.2 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2026-07-24 · updated 2026-08-24
• Weakness: CWE-444

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.

Affected products

• GNOME libsoup: all versions
• Red Hat Enterprise Linux: 6.0, 7.0, 8.0, 9.0, 10.0

References

• https://access.redhat.com/security/cve/CVE-2026-66338
• https://bugzilla.redhat.com/show_bug.cgi?id=2506950

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