# CVE-2026-123535: Tornado cookie attribute injection in set_cookie max_age

Source: https://junglewise.ai/threats/cve-2026-123535-tornado-before-6-6-does-not-validate-the-max-age-argument-of  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-08. Updated: 2026-11-08  
License: CC BY 4.0 with a link back

CVE-2026-123535 · Severity: medium · CVSS 4.2 · Published 2026-11-08

Tornado, a Python web framework, fails to validate the max_age argument when setting cookies, allowing attackers to inject additional cookie attributes. An attacker who can control the max_age parameter could expand a cookie's scope to unintended paths or subdomains, potentially enabling account takeover or session hijacking attacks if an application uses untrusted input.

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

## Quick answers

**Is CVE-2026-123535 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-123535 being exploited in the wild.

**How severe is CVE-2026-123535?** Medium severity, with a CVSS score of 4.2, published 8 November 2026.

**Which products and versions are affected?** Tornado before 6.6.

**Is there a fix for CVE-2026-123535?** Yes: fixed in 6.6.0. Until then: Convert the max_age argument to an integer (using int()) before passing it to set_cookie, set_signed_cookie, set_secure_cookie, or clear_cookie. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-123535 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-123535?** Check whether you run Tornado 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

- Fixed in 6.6.0

Convert the max_age argument to an integer (using int()) before passing it to set_cookie, set_signed_cookie, set_secure_cookie, or clear_cookie.

## Technical details

The RequestHandler.set_cookie method (and its wrappers set_signed_cookie, set_secure_cookie, and clear_cookie) does not validate or convert the max_age argument to an integer before including it in the Set-Cookie HTTP header. An attacker providing a malicious string like "86400; Domain=example.com" as max_age can inject arbitrary Set-Cookie attributes. The vulnerability affects applications that pass untrusted string input directly; those converting to int() first are unaffected.

## Affected products

- Tornado Tornado before 6.6

## Timeline

- 2026-10-22: disclosed: GitHub Security Advisory published
- 2026-11-08: advisory: CVE-2026-123535 and NVD entry published

## References

- [https://github.com/tornadoweb/tornado/security/advisories/GHSA-c6v4-qj2h-f748](https://github.com/tornadoweb/tornado/security/advisories/GHSA-c6v4-qj2h-f748)
- [https://www.vulncheck.com/advisories/tornado-before-6.6-cookie-attribute-injection-via-set-cookie-max-age](https://www.vulncheck.com/advisories/tornado-before-6.6-cookie-attribute-injection-via-set-cookie-max-age)

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