CVE-2025-67725: Tornado · Quadratic DoS via Repeated Header Coalescing
Affects nvcheckerSource GCVE Database
Not known to be exploited · CVSS 7.5 High : upgrade to 2.20 soon.
Data as of 26 Oct 2026, 06:26 UTC
- EPSS
- 0.5% chance of exploitation in 30 days – higher than 46% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- Patch
- Available – fixed in 2.2.2_3, 2.20
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HExploitation evidence
Disclosed: evidence found.
CVE published 12 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-26.
What to do
Upgrade nvchecker to 2.20; snakeviz to 2.2.2_3.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Homebrewsnakevizpkg:brew/snakevizOther threats | Affected
| Fixed in
|
Homebrewnvcheckerpkg:brew/nvcheckerOther threats | Affected
| Fixed in
|
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
A patch is available from Red Hat addressing this vulnerability in affected packages. Users should apply the official updates provided by Red Hat as detailed in the advisory RHSA-2026:0930. No additional mitigation actions are specified or required beyond applying the patch.
Description
CVE-2025-67725 is a high-severity Denial of Service (DoS) vulnerability in Tornado's HTTPHeaders.add method. The vulnerability arises from repeated header names causing quadratic time complexity due to string concatenation in Python, which can block Tornado's single event loop and disrupt service. The impact is more severe if the max_header_size setting is increased beyond its default 64KB. A patch addressing this issue is available from Red Hat for affected packages.
References
- access.redhat.com/errata/RHSA-2026:0930 (opens in a new tab)
- access.redhat.com/security/updates/classification/ (opens in a new tab)
- bugzilla.redhat.com/show_bug.cgi?id=2421722 (opens in a new tab)
- bugzilla.redhat.com/show_bug.cgi?id=2421733 (opens in a new tab)
- security.access.redhat.com/data/csaf/v2/advisories/2026/rhsa-2026_0930.json (opens in a new tab)
- github.com/tornadoweb/tornado/security/advisories/GHSA-c98p-7wgm-6p64 (opens in a new tab)
- nvd.nist.gov/vuln/detail/CVE-2025-67725 (opens in a new tab)
- github.com/tornadoweb/tornado/commit/771472cfdaeebc0d89a9cc46e249f8891a6b29cd (opens in a new tab)
- github.com/pypa/advisory-database/tree/main/vulns/tornado/PYSEC-2025-266.yaml (opens in a new tab)
- github.com/tornadoweb/tornado (opens in a new tab)
- github.com/tornadoweb/tornado/releases/tag/v6.5.3 (opens in a new tab)