--- id: CVE-2025-67726 title: Tornado is a Python web framework and asynchronous networking library summary: >- Tornado is a Python web framework and asynchronous networking library. Versions 6.5.2 and below use an inefficient algorithm when parsing parameters for HTTP header values, potentially causing a DoS. The _parseparam function in httputil.… severity: high cvss: 7.5 cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H' cwe: - CWE-400 - CWE-834 - CWE-1333 vendor: tornadoweb product: tornado affected: - tornado < 6.5.3 patched: - tornado 6.5.3 published: '2025-12-12' updated: '2026-10-07' sourceUpdated: '2026-10-07T20:10:01.970' source: NVD sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2025-67726' references: - url: >- https://github.com/tornadoweb/tornado/commit/771472cfdaeebc0d89a9cc46e249f8891a6b29cd label: security-advisories@github.com - url: 'https://github.com/tornadoweb/tornado/releases/tag/v6.5.3' label: security-advisories@github.com - url: >- https://github.com/tornadoweb/tornado/security/advisories/GHSA-jhmp-mqwm-3gq8 label: security-advisories@github.com - url: >- https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-67726.json - url: 'https://access.redhat.com/security/cve/CVE-2025-67726' - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2421733' - url: 'https://www.cve.org/CVERecord?id=CVE-2025-67726' - url: 'https://nvd.nist.gov/vuln/detail/CVE-2025-67726' - url: 'https://access.redhat.com/errata/RHSA-2026:0930' - url: 'https://access.redhat.com/errata/RHSA-2026:2462' - url: 'https://access.redhat.com/errata/RHSA-2026:2469' - url: 'https://access.redhat.com/errata/RHSA-2026:2465' - url: 'https://access.redhat.com/errata/RHSA-2026:2484' - url: 'https://access.redhat.com/errata/RHSA-2026:2106' - url: 'https://access.redhat.com/errata/RHSA-2026:3713' tags: - nvd - osv - pip - csaf - vex - red-hat - score-dispute epss: 0.00535 epssPercentile: 0.44976 aliases: - PYSEC-2025-267 - GHSA-jhmp-mqwm-3gq8 ecosystem: pip ingestedAt: '2026-07-13T18:58:06.943Z' scores: nvd: 7.5 vendor: 5.3 --- ## Overview Tornado is a Python web framework and asynchronous networking library. Versions 6.5.2 and below use an inefficient algorithm when parsing parameters for HTTP header values, potentially causing a DoS. The _parseparam function in httputil.py is used to parse specific HTTP header values, such as those in multipart/form-data and repeatedly calls string.count() within a nested loop while processing quoted semicolons. If an attacker sends a request with a large number of maliciously crafted parameters in a Content-Disposition header, the server's CPU usage increases quadratically (O(n²)) during parsing. Due to Tornado's single event loop architecture, a single malicious request can cause the entire server to become unresponsive for an extended period. This issue is fixed in version 6.5.3. ## Affected - `tornado < 6.5.3` ## Remediation Upgrade past the affected range: - `tornado 6.5.3` ## Package advisory (CVE-2025-67726) Affected packages: - `tornado < 6.5.3` Patched in: - `tornado 6.5.3` Source: https://osv.dev/vulnerability/PYSEC-2025-267 ## Vendor advisories - **RHSA-2026:0930** · Red Hat · fixed in: Red Hat Enterprise Linux HighAvailability (v. 8), Red Hat Enterprise Linux ResilientStorage (v. 8) · released 2026-01-21 · [advisory](https://access.redhat.com/errata/RHSA-2026:0930) - **RHSA-2026:2462** · Red Hat · fixed in: Red Hat Enterprise Linux High Availability AUS (v.8.4), Red Hat Enterprise Linux HighAvailability EUS EXTENSION (v.8.4) · released 2026-02-10 · [advisory](https://access.redhat.com/errata/RHSA-2026:2462) - **RHSA-2026:2469** · Red Hat · fixed in: Red Hat Enterprise Linux High Availability E4S (v.8.6), Red Hat Enterprise Linux High Availability TUS (v.8.6) · released 2026-02-10 · [advisory](https://access.redhat.com/errata/RHSA-2026:2469) - **RHSA-2026:2465** · Red Hat · fixed in: Red Hat Enterprise Linux High Availability E4S (v.8.8), Red Hat Enterprise Linux High Availability TUS (v.8.8) · released 2026-02-10 · [advisory](https://access.redhat.com/errata/RHSA-2026:2465) - **RHSA-2026:2484** · Red Hat · fixed in: Red Hat Enterprise Linux High Availability E4S (v.9.0), Red Hat Enterprise Linux ResilientStorage E4S (v.9.0) · released 2026-02-10 · [advisory](https://access.redhat.com/errata/RHSA-2026:2484) - **RHSA-2026:2106** · Red Hat · fixed in: Red Hat OpenShift AI 2.25 · released 2026-02-05 · [advisory](https://access.redhat.com/errata/RHSA-2026:2106) - **RHSA-2026:3713** · Red Hat · fixed in: Red Hat OpenShift AI 3.3 · released 2026-03-04 · [advisory](https://access.redhat.com/errata/RHSA-2026:3713) - **Red Hat VEX** · Moderate · affected: external secrets operator for Red Hat OpenShift - Tech Preview, Red Hat Advanced Cluster Security 4, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 9, Red Hat Enterprise Linux AI (RHEL AI) 3 · no fix planned: external secrets operator for Red Hat OpenShift - Tech Preview, Red Hat Advanced Cluster Security 4, Red Hat Enterprise Linux AI (RHEL AI) 3, Red Hat Enterprise Linux 10, … · updated 2026-10-09 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2025/cve-2025-67726.json)