CVE-2026-91992: Tornado before 6.5.7 Credential Leak via Handle Reuse
Tornado before 6.5.7 contains a credential leak vulnerability in CurlAsyncHTTPClient where pycurl handles are reused across requests without proper state clearing. Attackers can obtain sensitive credentials by issuing requests through the same client instance, allowing TLS certificates or proxy authentication to persist across unintended requests.
Affected Software
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Deployments using Tornado before 6.5.7 with CurlAsyncHTTPClient are affected. The issue arises when pycurl handles are reused across requests through the same client instance.
What must an attacker be able to do to exploit it?
An attacker needs to cause requests to be issued through the same CurlAsyncHTTPClient instance. Exploitation relies on reused pycurl handle state causing TLS certificates or proxy authentication to persist into unintended requests.
What sensitive data could be disclosed?
Sensitive credentials may leak between requests, including TLS certificates and proxy authentication credentials. The stated impact is confidentiality only; integrity and availability are not affected.
How can this be remediated?
Upgrade Tornado to version 6.5.7 or later. This version boundary is identified as fixing the handle-state clearing issue.