# CVE-2026-49853: Tornado SimpleAsyncHTTPClient sensitive header exposure in redirects

Source: https://junglewise.ai/threats/cve-2026-49853-tornado-simpleasynchttpclient-sensitive-header-exposure-in  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-14. Updated: 2026-07-14  
License: CC BY 4.0 with a link back

CVE-2026-49853 · Severity: high · CVSS 7.7 · Published 2026-07-14

Tornado, a popular Python web framework and networking library, contained a flaw in how it handled web redirects. When a program using Tornado's HTTP client was redirected to a different website, it would mistakenly send the original site's login credentials and cookies to the new, potentially malicious destination. This could allow an attacker to steal sensitive authentication tokens or user session data by tricking a service into following a redirect to a server they control.

Technologies: [tornado (PyPI)](https://junglewise.ai/threats/technologies/tornado). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## 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

  ```sh
  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

## References

- [https://github.com/tornadoweb/tornado/commit/aba2569f7ed7a6bdbef816658fb6b7182531b751](https://github.com/tornadoweb/tornado/commit/aba2569f7ed7a6bdbef816658fb6b7182531b751)
- [https://github.com/tornadoweb/tornado/pull/3626](https://github.com/tornadoweb/tornado/pull/3626)
- [https://github.com/tornadoweb/tornado/releases/tag/v6.5.6](https://github.com/tornadoweb/tornado/releases/tag/v6.5.6)
- [https://github.com/tornadoweb/tornado/security/advisories/GHSA-3x9g-8vmp-wqvf](https://github.com/tornadoweb/tornado/security/advisories/GHSA-3x9g-8vmp-wqvf)

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