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    CVE-2026-66338

    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.

    Published:Jul 24, 2026
    Last Modified:Aug 24, 2026
    EPS:Jul 24, 2026
    EPSS Score:0.00174
    CVSS Score:5.4

    Affected Products

    Vendor
    Gnome
    Product
    Libsoup
    Vendor
    Libsoup
    Product
    Libsoup
    Vendor
    Redhat
    Product
    Enterprise Linux

    Exploits

    https://bugzilla.redhat.com/show_bug.cgi?id=2506950

    Common Attack Pattern Enumeration and Classification (CAPEC)

    CAPEC-273 HTTP Response Smuggling
    CAPEC-33 HTTP Request Smuggling

    Related CVEs

    CVE-2026-85534 (CVSS 5.9) — A flaw was found in libsoup. When a client sends an HTTP/2 request body from a non-pollable input stream, the …
    CVE-2026-66337 (CVSS 6.5) — A flaw was found in libsoup. An unsigned integer underflow in the soup_filter_input_stream_read_until() functi…
    CVE-2026-66339 (CVSS 6.5) — A flaw was found in libsoup. After a CONNECT tunnel is established through an HTTP proxy, libsoup incorrectly …
    CVE-2026-12548 (CVSS 4.2) — A heap out-of-bounds read flaw was found in libsoup. When parsing multipart HTTP messages, an integer type mis…
    CVE-2026-6324 (CVSS 4.8) — A flaw was found in libsoup. A remote attacker could exploit an unsigned to signed conversion error in the `so…
    CVE-2026-5119 (CVSS 5.9) — A flaw was found in libsoup. When establishing HTTPS tunnels through a configured HTTP proxy, sensitive sessio…
    CVE-2026-4271 (CVSS 5.3) — A flaw was found in libsoup, a library for handling HTTP requests. This vulnerability, known as a Use-After-Fr…
    CVE-2026-3633 (CVSS 3.9) — A flaw was found in libsoup. A remote attacker, by controlling the method parameter of the `soup_message_new()…
    CVE-2026-3632 (CVSS 3.9) — A flaw was found in libsoup, a library used by applications to send network requests. This vulnerability occur…
    CVE-2026-3634 (CVSS 3.9) — A flaw was found in libsoup. An attacker controlling the value used to set the Content-Type header can inject …

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High