Amazon Linux 2 : libsoup (ALAS-2026-3970)

high Nessus Plugin ID 365200

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Synopsis

The remote Amazon Linux 2 host is missing a security update.

Description

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.

Solution

Run 'yum update libsoup' or or 'yum update --advisory ALAS2-2026-3970' to update your system.

Plugin Details

Severity: High

ID: 365200

File Name: al2_ALAS-2026-3970.nasl

Version: 1.1

Type: Local

Agent: unix

Family: Amazon Linux Local Security Checks

Published: 10/12/2026

Updated: 10/12/2026

Supported Sensors: Frictionless Assessment AWS, Frictionless Assessment Agent, Nessus Agent, Agentless Assessment, Continuous Assessment, Tenable Cloud Security, Tenable Self-Hosted Container Security, Nessus

Risk Information

VPR

Risk Factor: Medium

Score: 4.3

Percentile: 53.51

CVSS v2

Risk Factor: Medium

Base Score: 6.4

Temporal Score: 5

Vector: CVSS2#AV:N/AC:L/Au:N/C:P/I:P/A:N

CVSS Score Source: CVE-2026-66338

CVSS v3

Risk Factor: High

Base Score: 7.2

Temporal Score: 6.5

Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

Temporal Vector: CVSS:3.0/E:P/RL:O/RC:C

Vulnerability Information

CPE: cpe:/o:amazon:linux:2, p-cpe:/a:amazon:linux:libsoup-debuginfo, p-cpe:/a:amazon:linux:libsoup-devel, p-cpe:/a:amazon:linux:libsoup

Required KB Items: Host/local_checks_enabled, Host/AmazonLinux/release, Host/AmazonLinux/rpm-list

Exploit Available: true

Exploit Ease: Exploits are available

Patch Publication Date: 10/12/2026

Vulnerability Publication Date: 1/13/2026

Reference Information

CVE: CVE-2026-0716, CVE-2026-12478, CVE-2026-12547, CVE-2026-12548, CVE-2026-12549, CVE-2026-66337, CVE-2026-66338, CVE-2026-66339, CVE-2026-77014, CVE-2026-77680

IAVA: 2026-A-0139-S, 2026-A-0555-S, 2026-A-0894

Detections

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