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.

It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2023-2026-3212 advisory.

    A flaw was found in libsoup. When handling an incoming WebSocket Pong frame, SoupWebsocketConnection     emitted the ::pong signal with a GByteArray pointer even though the signal is declared to pass a GBytes.
    Applications connecting a handler that follows the documented GBytes API can trigger heap corruption or a     crash upon receiving a crafted Pong. (CVE-2026-102556)

    A flaw was found in libsoup. When reassembling fragmented WebSocket messages into a GByteArray, libsoup     did not adequately cap total message size against the limits of the underlying buffer type. A remote peer     could send fragments that caused size truncation while the implementation still used the full length,     leading to heap corruption or a crash. (CVE-2026-102557)

    A flaw was found in libsoup. When max-incoming-payload-size is unlimited (0), SoupWebsocketConnection     could grow its incoming GByteArray based on an attacker-controlled frame length until the length wrapped,     causing a heap buffer overflow while reading frame data. (CVE-2026-102558)

    A flaw was found in libsoup. When constructing a masked WebSocket client frame for a very large outgoing     payload, size values passed to GByteArray allocation APIs could be truncated while the masking routine     still used the full length, causing a heap buffer overflow. (CVE-2026-102559)

    A flaw was found in libsoup. When the permessage-deflate WebSocket extension compresses a very large     outgoing message, truncated size calculations used for GByteArray growth could wrap, causing zlib to write     past the allocated buffer and resulting in a heap buffer overflow. (CVE-2026-102560)

    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. (CVE-2026-103399)

    An out-of-bounds read vulnerability was found in libsoup's multipart processing subsystem. The flaw exists     in the soup_multipart_input_stream_read_headers() function inside soup-multipart-input-stream.c, which     does not adequately restrict or validate the size of incoming multipart boundary strings. When processing     a crafted HTTP response containing a malformed or oversized boundary parameter, the internal stream reader     reads past the allocated buffer bounds. A remote, unauthenticated attacker can exploit this behavior to     cause a service denial (DoS) through application failure or potentially read fragments of unauthorized     memory metadata. (CVE-2026-15714)

    A flaw was found in libsoup. An unsigned integer underflow in the soup_filter_input_stream_read_until()     function causes a heap buffer over-read when parsing multipart HTTP responses. A malicious HTTP server can     exploit this by sending a crafted multipart response, potentially causing the client application to crash     or disclose sensitive heap memory. (CVE-2026-66337)

    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. (CVE-2026-66338)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The version of libsoup installed on the remote host is prior to 2.56.0-6. It is, therefore, affected by multiple vulnerabilities as referenced in the ALAS2-2026-3970 advisory.

    OOB Read via Integer Overflow on libsoup through libsoup/websocket/soup-websocket-connection.c via     process_frame() leads to Undefined Behavior (CVE-2026-0716)

    The fix for CVE-2026-0716 (commit 6ff7ef0, libsoup 3.6.6) placed the integer overflow guard inside the if     (masked) block, leaving unmasked server-to-client frames unprotected. A malicious WebSocket server can     send a crafted unmasked frame with a payload length near UINT64_MAX to trigger an OOB read in a libsoup-     based client when max_incoming_payload_size is set to 0. (CVE-2026-12478)

    SoupAuthManager caches proxy authentication credentials without scoping them to the proxy authority     (host:port). When the proxy configuration changes (e.g., via system settings or WPAD), cached Proxy-     Authorization headers from the previous proxy are sent to the new proxy, leaking credentials.
    (CVE-2026-12547)

    A heap out-of-bounds read flaw was found in libsoup. When parsing multipart HTTP messages, an integer type     mismatch between the caller and soup_headers_parse() can cause the length parameter to be incorrectly     truncated, leading to a heap buffer over-read. A remote attacker could use this flaw to crash an     application using libsoup or potentially disclose heap memory contents. (CVE-2026-12548)

    The fix for CVE-2026-2443 was regressed by a subsequent rework commit that replaced specific overflow     checks with a general signed comparison. When a client sends a Range request with a suffix length     exceeding the content size, the resulting negative start value is not properly clamped, leading to     malformed HTTP 206 responses and log flooding. (CVE-2026-12549)

    A flaw was found in libsoup. An unsigned integer underflow in the soup_filter_input_stream_read_until()     function causes a heap buffer over-read when parsing multipart HTTP responses. A malicious HTTP server can     exploit this by sending a crafted multipart response, potentially causing the client application to crash     or disclose sensitive heap memory. (CVE-2026-66337)

    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. (CVE-2026-66338)

    A flaw was found in libsoup. After a CONNECT tunnel is established through an HTTP proxy, libsoup     incorrectly attaches the Proxy-Authorization header to subsequent HTTPS requests sent through that tunnel     to the destination server. This allows the destination server to capture proxy credentials, leading to     information disclosure. (CVE-2026-66339)

    A flaw was found in libsoup's SoupServer HTTP Range header processing. The sort_ranges() comparator in     soup-message-headers.c truncates a 64-bit subtraction result to 32-bit int, flipping the sign for range     offsets differing by more than INT_MAX. This causes silent omission of requested byte ranges from HTTP 206     Partial Content responses on resources larger than approximately 2 GB. (CVE-2026-77014)

    An algorithmic complexity flaw exists in libsoup's HTTP Range header processing that persists after the     CVE-2025-32907 fix.

    CVE-2025-32907 addressed memory amplification when a client repeated the same range many times in a single     Range header. Commit 9bb92f7a corrected merge correctness in soup_message_headers_get_ranges_internal() in     libsoup/soup-message-headers.c, but the coalescing loop still removes merged ranges using     g_array_remove_index() for each coalesced element. Because GArray is contiguous, each mid-array removal     performs an O(N) memmove. When many identical satisfiable ranges are supplied (for example bytes=0-0     repeated thousands of times), the loop performs O(N2) work coalescing them into a single range.

    The vulnerable path is reachable server-side from handle_partial_get() in libsoup/server/http1/soup-     server-message-io-http1.c when a SoupServer handler returns HTTP 200 with a non-empty body. No     authentication is required. The number of ranges is bounded only by the maximum request header size (~100     KiB), allowing roughly 25,000 ranges per request. Reporter measurements on libsoup HEAD containing the     CVE-2025-32907 fix show ~90 ms single-core CPU per such request at the wire maximum, blocking the server's     event loop for that duration.

    This is a CPU exhaustion / availability issue only. No memory corruption or information disclosure occurs.

    Affected: libsoup versions containing the CVE-2025-32907 fix but not merge request !550.Fixed upstream: MR     !550 merged 2026-08-20, replacing per-element removal with O(N) in-place compaction and rejecting Range     headers requesting more than 200 ranges.Upstream report:
    https://gitlab.gnome.org/GNOME/libsoup/-/issues/538Related: CVE-2025-32907 (CVE-2026-77680)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - 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. (CVE-2026-66338)

The AlmaLinux 9.2 host has packages installed that are affected by multiple vulnerabilities as referenced in the TuxCare ALMALINUX9.2:CLSA-2026:1788856994 advisory.

  - A heap out-of-bounds read flaw was found in libsoup. When parsing multipart HTTP messages, an integer type     mismatch between the caller and soup_headers_parse() can cause the length parameter to be incorrectly     truncated, leading to a heap buffer over-read. A remote attacker could use this flaw to crash an     application using libsoup or potentially disclose heap memory contents. (CVE-2026-12548)

  - A flaw was found in libsoup. An unsigned integer underflow in the soup_filter_input_stream_read_until()     function causes a heap buffer over-read when parsing multipart HTTP responses. A malicious HTTP server can     exploit this by sending a crafted multipart response, potentially causing the client application to crash     or disclose sensitive heap memory. (CVE-2026-66337)

  - 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. (CVE-2026-66338)

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The CentOS Linux 7 host has packages installed that are affected by a vulnerability as referenced in the TuxCare CENTOS7:CLSA-2026:1787751026 advisory.

  - 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. (CVE-2026-66338)

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

The Rocky Linux 9.6 host has packages installed that are affected by a vulnerability as referenced in the TuxCare ALMALINUX9.6:CLSA-2026:1787783675 advisory.

  - 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. (CVE-2026-66338)

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

The AlmaLinux 9.6 host has packages installed that are affected by a vulnerability as referenced in the TuxCare ALMALINUX9.6:CLSA-2026:1787783675 advisory.

  - 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. (CVE-2026-66338)

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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. (CVE-2026-66338)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Type	Severity
365275	Amazon Linux 2023 : libsoup, libsoup-devel (ALAS2023-2026-3212)	Nessus	Amazon Linux Local Security Checks	Local	high
365200	Amazon Linux 2 : libsoup (ALAS-2026-3970)	Nessus	Amazon Linux Local Security Checks	Local	high
473743	Echo: libsoup3: security update to 3.6.6-1+e12	Tenable Cloud Security	Echo Local Security Checks	Local	high
473743	Echo: libsoup3: security update to 3.6.6-1+e12	Tenable Self-Hosted Container Security	Echo Local Security Checks	Local	high
362316	AlmaLinux 9.2 [TuxCare] Security Update: libsoup / libsoup-devel / libsoup-doc Multiple Vulnerabilities (ALMALINUX9.2:CLSA-2026:1788856994)	Nessus	Alma Linux Local Security Checks	Local	high
352853	CentOS Linux 7 [TuxCare] Security Update: libsoup / libsoup-devel (CENTOS7:CLSA-2026:1787751026)	Nessus	CentOS Local Security Checks	Local	high
351735	Rocky Linux 9.6 [TuxCare] Security Update: libsoup / libsoup-devel / libsoup-doc (ALMALINUX9.6:CLSA-2026:1787783675)	Nessus	Rocky Linux Local Security Checks	Local	high
351702	AlmaLinux 9.6 [TuxCare] Security Update: libsoup / libsoup-devel / libsoup-doc (ALMALINUX9.6:CLSA-2026:1787783675)	Nessus	Alma Linux Local Security Checks	Local	high
329641	Linux Distros Unpatched Vulnerability : CVE-2026-66338	Nessus	Misc.	Local	high

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