ALAS2027-2026-215

References: CVE-2026-66338  CVE-2026-66337  CVE-2026-103399 
FAQs regarding Amazon Linux ALAS/CVE Severity

Issue Overview:

Package updates are available for Amazon Linux 2027 that fix the following vulnerabilities:
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.

CVE-2026-66337:
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-2026-103399:
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.

Issue Correction:
Run dnf update libsoup3 or dnf update --advisory ALAS2027-2026-215 to update your system.

New Packages:

aarch64:
    libsoup3-debuginfo-3.7.3-2.amzn2027.aarch64
    libsoup3-devel-3.7.3-2.amzn2027.aarch64
    libsoup3-3.7.3-2.amzn2027.aarch64
    libsoup3-debugsource-3.7.3-2.amzn2027.aarch64

noarch:
    libsoup3-doc-3.7.3-2.amzn2027.noarch

src:
    libsoup3-3.7.3-2.amzn2027.src

x86_64:
    libsoup3-debuginfo-3.7.3-2.amzn2027.x86_64
    libsoup3-debugsource-3.7.3-2.amzn2027.x86_64
    libsoup3-devel-3.7.3-2.amzn2027.x86_64
    libsoup3-3.7.3-2.amzn2027.x86_64