Amazon Linux 2027 Preview Security Advisory: ALAS2027-2026-101
Advisory Release Date: 2026-09-28 09:00 Pacific
Advisory Updated Date: 2026-09-28 09:00 Pacific
Tornado is a Python web framework and asynchronous networking library. Prior to 6.5.8, Tornado parses application/x-www-form-urlencoded request bodies with urllib.parse.parse_qs in tornado/escape.py without passing max_num_fields. RequestHandler._execute in tornado/web.py parses the body before handler dispatch through HTTPServerRequest._parse_body and parse_body_arguments in tornado/httputil.py, so an unauthenticated request body containing millions of separator-delimited fields can synchronously stall the single-threaded event loop and delay every connection. The body is bounded only by max_buffer_size, which defaults to 104857600 bytes. This issue is fixed in version 6.5.8. (CVE-2026-82397)
Tornado before 6.5.8 contains an incomplete fix for cookie attribute injection that allows attackers to inject arbitrary cookie attributes by passing capitalized or legacy keyword arguments to set_cookie. Attackers can embed semicolon-delimited data in capitalized parameters like Domain, Path, or SameSite to bypass validation and modify cookie security attributes. (CVE-2026-91991)
Affected Packages:
python-tornado
Issue Correction:
Run yum update python-tornado to update your system.
aarch64:
python-tornado-debugsource-6.5.8-1.amzn2027.0.1.aarch64
python-tornado-doc-6.5.8-1.amzn2027.0.1.aarch64
python3-tornado-debuginfo-6.5.8-1.amzn2027.0.1.aarch64
python3-tornado-6.5.8-1.amzn2027.0.1.aarch64
src:
python-tornado-6.5.8-1.amzn2027.0.1.src
x86_64:
python3-tornado-debuginfo-6.5.8-1.amzn2027.0.1.x86_64
python-tornado-debugsource-6.5.8-1.amzn2027.0.1.x86_64
python-tornado-doc-6.5.8-1.amzn2027.0.1.x86_64
python3-tornado-6.5.8-1.amzn2027.0.1.x86_64