CVE-2026-91991: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting') in tornadoweb tornado
CVE-2026-91991 is a vulnerability in Tornado versions 6.5.5 up to but not including 6.5.8. It involves an incomplete fix for cookie attribute injection that allows attackers to inject arbitrary cookie attributes by using capitalized or legacy keyword arguments in the set_cookie function. This enables attackers to embed semicolon-delimited data in parameters such as Domain, Path, or SameSite, bypassing validation and potentially modifying cookie security attributes.
AI Analysis
Technical Summary
Tornado before version 6.5.8 contains an incomplete fix for cookie attribute injection. Attackers can exploit this by passing capitalized or legacy keyword arguments to the set_cookie method, allowing injection of arbitrary cookie attributes. Specifically, semicolon-delimited data can be embedded in capitalized parameters like Domain, Path, or SameSite, bypassing validation mechanisms and enabling modification of cookie security attributes. This vulnerability is classified as HTTP Request/Response Splitting due to improper neutralization of CRLF sequences in HTTP headers.
Potential Impact
An attacker exploiting this vulnerability can manipulate cookie attributes, potentially weakening cookie security controls such as domain, path, or SameSite policies. This could lead to security issues like session fixation or cross-site request forgery (CSRF) bypasses. The CVSS 4.0 score is 6.3 (medium severity), indicating that exploitation requires network access with high attack complexity and partial impact on confidentiality and integrity.
Mitigation Recommendations
A fix is available in Tornado version 6.5.8 and later. Users should upgrade to version 6.5.8 or newer to fully address this vulnerability. No additional mitigations are specified by the vendor advisory. Patch status is confirmed by the affectedVersions data indicating the vulnerability affects versions >=6.5.5 and <6.5.8.
CVE-2026-91991: Improper Neutralization of CRLF Sequences in HTTP Headers ('HTTP Request/Response Splitting') in tornadoweb tornado
Description
CVE-2026-91991 is a vulnerability in Tornado versions 6.5.5 up to but not including 6.5.8. It involves an incomplete fix for cookie attribute injection that allows attackers to inject arbitrary cookie attributes by using capitalized or legacy keyword arguments in the set_cookie function. This enables attackers to embed semicolon-delimited data in parameters such as Domain, Path, or SameSite, bypassing validation and potentially modifying cookie security attributes.
CVSS v4.0
Score 6.3medium
Affected software
tornadoweb
tornado
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AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
Tornado before version 6.5.8 contains an incomplete fix for cookie attribute injection. Attackers can exploit this by passing capitalized or legacy keyword arguments to the set_cookie method, allowing injection of arbitrary cookie attributes. Specifically, semicolon-delimited data can be embedded in capitalized parameters like Domain, Path, or SameSite, bypassing validation mechanisms and enabling modification of cookie security attributes. This vulnerability is classified as HTTP Request/Response Splitting due to improper neutralization of CRLF sequences in HTTP headers.
Potential Impact
An attacker exploiting this vulnerability can manipulate cookie attributes, potentially weakening cookie security controls such as domain, path, or SameSite policies. This could lead to security issues like session fixation or cross-site request forgery (CSRF) bypasses. The CVSS 4.0 score is 6.3 (medium severity), indicating that exploitation requires network access with high attack complexity and partial impact on confidentiality and integrity.
Mitigation Recommendations
A fix is available in Tornado version 6.5.8 and later. Users should upgrade to version 6.5.8 or newer to fully address this vulnerability. No additional mitigations are specified by the vendor advisory. Patch status is confirmed by the affectedVersions data indicating the vulnerability affects versions >=6.5.5 and <6.5.8.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- VulnCheck
- Date Reserved
- 2026-09-15T11:11:13.311Z
- Cvss Version
- 4.0
- State
- PUBLISHED
Threat ID: 6aa9651e55bf5e2cf502eb37
Added to database: 09/15/2026, 15:32:46 UTC
Last enriched: 09/15/2026, 15:47:06 UTC
Last updated: 09/15/2026, 15:53:10 UTC
Views: 4
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