Quick answers
- Is CVE-2026-49853 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-49853 being exploited in the wild.
- How severe is CVE-2026-49853?
- High severity, with a CVSS score of 7.7, published 14 July 2026.
- Which products and versions are affected?
- tornado (PyPI) < 6.5.6, ECOSYSTEM:introduced=0,fixed=6.5.6.
- Is there a fix for CVE-2026-49853?
- Yes. tornado (PyPI): upgrade to 6.5.6 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-49853 attacked?
- It is attacked over the network, in a software library.
- Am I affected by CVE-2026-49853?
- Check whether you run tornado (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
How to fix
- tornado (PyPI): upgrade to 6.5.6 or later
pip install "tornado>=6.5.6"
Technical details
A vulnerability exists in Tornado's SimpleAsyncHTTPClient where redirected requests are shallow-copied without properly clearing sensitive headers. Specifically, when a 3xx redirect changes the scheme, host, or port (cross-origin), the client removes the 'Host' header but retains 'Authorization', 'Cookie', 'auth_username', 'auth_password', and 'auth_mode'. An attacker who can influence a URL requested by a Tornado-based application could redirect the client to a malicious server to capture these credentials. This issue is fixed in version 6.5.6, which now strips these headers on cross-origin redirects to match libcurl's behavior.
Affected products
- tornadoweb tornado < 6.5.6
Identifiers
- CVE-2026-49853
- GHSA-3x9g-8vmp-wqvf
- PYSEC-2026-3387
Timeline
- 2026-05-27: patched: Fixed in version 6.5.6
- 2026-05-27: advisory: GitHub Security Advisory published
- 2026-07-14: disclosed: CVE published to NVD