Tornado is a Python web framework and asynchronous networking library. In versions 6.5.2 and below, a single maliciously crafted HTTP request can block the server's event loop for an extended period, caused by the HTTPHeaders.add method. The function accumulates values using string concatenation when the same header name is repeated, causing a Denial of Service (DoS). Due to Python string immutability, each concatenation copies the entire string, resulting in O(n²) time complexity. The severity can vary from high if max_header_size has been increased from its default, to low if it has its default value of 64KB. This issue is fixed in version 6.5.3.
CVE-2025-67725
This high-severity CVE scores 7.5 under NVD CVSS v3. EPSS exploit probability: 0.2%, top 56% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).
- High severity, but no confirmed exploitation yet
A fix is available — apply it.
- CVSS v3
- 7.5
- EG Score
- 7.5(medium)
- EPSS
- 32.6%
- KEV
- Not listed
Published
December 12, 2025
Last Modified
June 17, 2026
References (3)
- security-advisories@githubhttps://github.com/tornadoweb/tornado/commit/771472cfdaeebc0d89a9cc46e249f8891a6b29cd
- security-advisories@githubhttps://github.com/tornadoweb/tornado/releases/tag/v6.5.3
- security-advisories@githubhttps://github.com/tornadoweb/tornado/security/advisories/GHSA-c98p-7wgm-6p64
Vendor Advisories for CVE-2025-67725(7)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
- RHSA-2026:3713Red Hat Product SecurityCritical
Red Hat Security Advisory: RHOAI 3.3 - Red Hat OpenShift AI
- RHSA-2026:2484Red Hat Product SecurityHigh
Red Hat Security Advisory: pcs security update
- RHSA-2026:2469Red Hat Product SecurityHigh
Red Hat Security Advisory: pcs security update
- RHSA-2026:2465Red Hat Product SecurityHigh
Red Hat Security Advisory: pcs security update
- RHSA-2026:2462Red Hat Product SecurityHigh
Red Hat Security Advisory: pcs security update
- RHSA-2026:2106Red Hat Product SecurityHigh
Red Hat Security Advisory: RHOAI 2.25.2 - Red Hat OpenShift AI
- RHSA-2026:0930Red Hat Product SecurityMedium
Red Hat Security Advisory: pcs security update
Patch Availability(8)
| Vendor / Ecosystem | Fixed in / Patch | Released | Source |
|---|---|---|---|
| ubuntu | python3-tornado (6.1.0-3ubuntu0.1~esm4) @ jammy | 2026-05-29 | ubuntu |
| redhat | rhoai/odh-workbench-jupyter-trustyai-cpu-py312-rhel9:1771874181 | 2026-03-04 | redhat |
| redhat | pcs-0:0.11.1-10.el9_0.10 | 2026-02-10 | redhat |
| redhat | pcs-0:0.10.15-4.el8_8.10 | 2026-02-10 | redhat |
| redhat | pcs-0:0.10.8-1.el8_4.10 | 2026-02-10 | redhat |
| redhat | pcs-0:0.10.12-6.el8_6.12 | 2026-02-10 | redhat |
| redhat | rhoai/odh-workbench-jupyter-trustyai-cpu-py312-rhel9:1770055425 | 2026-02-05 | redhat |
| redhat | pcs-0:0.10.18-2.el8_10.8 | 2026-01-21 | redhat |
Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.
Affected Packages
(1 across 1 ecosystem)
PyPI(1)
| Package | Vulnerable range | Fixed in | Dependents |
|---|---|---|---|
| tornado | 0.2 ... 6.5b1 (78 versions) | 6.5.3 | — |
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Additional Vendor Advisories
(1)
Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.
Data Freshness Timeline
(refreshed 9× in last 7d / 47× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
- 2026-07-15 16:57 UTCEPSS rescore
- 2026-07-15 16:57 UTCEPSS rescore
- 2026-07-15 01:59 UTCEPSS rescore
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- 2026-07-06 07:41 UTCOSV refresh
- 2026-07-06 02:23 UTCEPSS rescore
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- 2026-06-30 23:22 UTCEPSS rescore
- 2026-06-29 14:06 UTCEPSS rescore
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- 2026-06-28 14:07 UTCEPSS rescore
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- 2026-06-17 19:35 UTCOSV refresh
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- 2026-05-31 00:16 UTCEPSS rescore
- 2026-05-31 00:16 UTCEPSS rescore
- 2026-05-29 17:40 UTCEG score recompute
- 2026-05-29 17:40 UTCVendor advisory
- 2026-05-29 13:44 UTCEPSS rescore
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Frequently asked(5)
What is CVE-2025-67725?
When was CVE-2025-67725 disclosed?
Is CVE-2025-67725 actively exploited?
What is the CVSS score of CVE-2025-67725?
How do I remediate CVE-2025-67725?
Dependency Blast Radius
See which npm, PyPI, Go, and Maven packages are affected by CVE-2025-67725
Is Your Infrastructure Affected by CVE-2025-67725?
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