Tornado before 6.5.8 contains an incomplete fix for cookie attribute injection that allows attackers to inject arbitrary cookie attributes by passing capitalized or legacy keyword arguments to set_cookie. Attackers can embed semicolon-delimited data in capitalized parameters like Domain, Path, or SameSite to bypass validation and modify cookie security attributes.
CVE-2026-91991
MEDIUMPre-NVD 5.45.4—Trending — 4 sources updated this week
EchelonGraph scoreHIGH confidence
Score 5.4 from GitHub Security Advisory published 2026-09-15. a secondary CVSS source baseline 5.4; sources differ by 0.0.
Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
5.4EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
- Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.4Exploit: None knownExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 5.4
- EG Score
- 5.4(high)
- EG Risk
- 29(Track)EG Risk 29/100SSVC: Track
EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).
How it’s computedSeverity54% × 45%Exploitation0% × 40%Automatability30% × 15%Action: Routine — remediate on your standard cadence. - EPSS PROB
- 0%
- EPSS %ILE
- 13%
- KEV
- Not listed
Published
September 15, 2026
Last Modified
September 16, 2026
Advisory Details (2)
Auto-updated Sep 15, 2026Patch available. Sources: github.
generic
Tornado before 6.5.8 Cookie Attribute Injection via Capitalized kwargs | Advisories | VulnCheck
https://www.vulncheck.com/advisories/tornado-before-6.5.8-cookie-attribute-injection-via-capitalized-kwargsgithub Patch Available
Incomplete fix for CVE-2026-35536: cookie attribute injection re-opened via the legacy case-insensitive `**kwargs` path in `set_cookie` · Advisory · tornadoweb/tornado · GitHub
https://github.com/tornadoweb/tornado/security/advisories/GHSA-wwv5-g3v4-889xVendor Advisories for CVE-2026-91991(1)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Affected Packages
(1 across 1 ecosystem)
PyPI(1)
| Package | Vulnerable range | Fixed in | Dependents |
|---|---|---|---|
| tornado | 6.5.5, 6.5.6, 6.5.7 | 6.5.8 | — |
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 12× in last 7d / 12× 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.
- 2026-09-18 19:28 UTCEPSS rescore
- 2026-09-18 14:19 UTCEG score recompute
- 2026-09-18 14:18 UTCGHSA enrichment
- 2026-09-17 19:32 UTCEPSS rescore
- 2026-09-17 14:01 UTCEG score recompute
- 2026-09-17 14:01 UTCGHSA enrichment
- 2026-09-16 14:09 UTCEPSS rescore
- 2026-09-16 13:45 UTCEG score recompute
- 2026-09-16 13:44 UTCGHSA enrichment
- 2026-09-15 16:32 UTCEG score recompute
- 2026-09-15 15:23 UTCEG score recompute
- 2026-09-15 15:22 UTCMITRE cvelistV5first tracked
Frequently asked(5)
What is CVE-2026-91991?
CVE-2026-91991 is a medium vulnerability published on September 15, 2026. Tornado before 6.5.8 contains an incomplete fix for cookie attribute injection that allows attackers to inject arbitrary cookie attributes by passing capitalized or legacy keyword arguments to set_cookie. Attackers can embed semicolon-delimited data in capitalized parameters like Domain, Path, or…
When was CVE-2026-91991 disclosed?
CVE-2026-91991 was first published in the National Vulnerability Database on September 15, 2026, with the most recent update on September 16, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-91991 actively exploited?
CVE-2026-91991 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 87.4% of all scored CVEs.
What is the CVSS score of CVE-2026-91991?
CVE-2026-91991 has a CVSS v3 base score of 5.4 (NVD).
How do I remediate CVE-2026-91991?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-91991, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.
Dependency Blast Radius
See which npm, PyPI, Go, and Maven packages are affected by CVE-2026-91991
Is Your Infrastructure Affected by CVE-2026-91991?
EchelonGraph automatically scans your cloud infrastructure and maps CVE exposure using blast radius analysis.