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  4. CVE 2026 66338 libsoup libsoup http request smuggling via
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Back to active CVEs
Medium · CVSS 5.4CVE-2026-66338

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

Answer in brief

CVE-2026-66338 records a Medium severity (CVSS 5.4) vulnerability in Libsoup: libsoup: http request smuggling via permissive chunk-size parsing in soup_body_input_stream_read_chunked(). The current sources do not mark it as known exploited. The current feed maps Red Hat/libsoup (generic), Red Hat/libsoup3 (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Jul 24, 2026Updated Nov 6, 2026Source checked Nov 6, 2026First seen by HOL Aug 26, 2026Material review Nov 6, 2026
Upstream Advisory

Key facts

Risk
Medium · CVSS 5.4
Exploitation
Not marked as known exploited
Affected software
8 mapped packages or products
Fix availability
Not reported

Why this deserves its current priority

CVSS is 5.4. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps Red Hat/libsoup (generic), Red Hat/libsoup3 (generic). Check affected ranges and fixed versions before updating.

Affected products and reported versions
ProductAffected versionsFixed versions
cpe:2.3:a:gnome:libsoup:-:*:*:*:*:*:*:*Not reportedNot reported
cpe:2.3:o:redhat:enterprise_linux:10.0:*:*:*:*:*:*:*Not reportedNot reported
cpe:2.3:o:redhat:enterprise_linux:6.0:*:*:*:*:*:*:*Not reportedNot reported
cpe:2.3:o:redhat:enterprise_linux:7.0:*:*:*:*:*:*:*Not reportedNot reported
cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:*Not reportedNot reported
cpe:2.3:o:redhat:enterprise_linux:9.0:*:*:*:*:*:*:*Not reportedNot reported
Mapped affected packages and fixed versions
PackageAffected rangeFixed version
Red Hat/libsoupgeneric*Not reported
Red Hat/libsoup3generic*Not reported

Recommended response

  1. 1Check inventory. Check lockfiles and deployed manifests for Red Hat/libsoup, Red Hat/libsoup3.
  2. 2Review the reported fix. Monitor this advisory for an available fix and review any installs of the affected package.

Evidence timeline and material changes

  1. Published upstream

    Jul 24, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  2. Source modified

    Nov 6, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  3. First seen by HOL

    Aug 26, 2026

Sources and claim methodology

  • Source referenceaccess.redhat.com
  • Source referencebugzilla.redhat.com
Upstream source 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.

Quoted source text, attributed separately from HOL analysis.

Record context

Vulnerability class
Vulnerability
EPSS
Not reported
CWE IDs
CWE-444
Source
CVE List V5
Source checked
Nov 6, 2026
References
2 linked sources
Open source record