Improper Neutralization of Special Elements in Output Used by a Downstream Component in Tornado - CVE-2026-123535
Published: November 9, 2026 / Updated: November 10, 2026
Vulnerability identifier: #VU162932
CSH Severity: Medium
CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N]
CVE-ID: CVE-2026-123535
CWE-ID: CWE-74
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows an unauthenticated remote attacker to alter cookie attributes and widen a cookie's scope to parent paths or other subdomains.
The vulnerability exists due to missing validation of the max_age argument in Tornado's RequestHandler.set_cookie when applications pass attacker-influenced strings without first converting them to integers. An unauthenticated remote attacker can supply a string containing additional cookie attributes that are incorporated into the resulting Set-Cookie header.
Affected software
Tornado
How to mitigate CVE-2026-123535
Install security update from vendor's website.
Tornado - update to 6.6.0