Pre-auth memory exhaustion via unbounded multipart splitting
Published Sep 15, 2026 · Updated Sep 15, 2026
Memory amplification in Tornado before 6.5.8 allows remote attackers to exhaust server memory with crafted multipart requests. parse_multipart_form_data materializes every boundary-delimited segment with bytes.split before enforcing max_parts, creating a large transient list from a relatively small body. Any unauthenticated HTTP endpoint that parses multipart/form-data is exposed, and successful exploitation can interrupt the service.
Summary
What happened
Memory amplification in Tornado before 6.5.8 allows remote attackers to exhaust server memory with crafted multipart requests. parse_multipart_form_data materializes every boundary-delimited segment with bytes.split before enforcing max_parts, creating a large transient list from a relatively small body. Any unauthenticated HTTP endpoint that parses multipart/form-data is exposed, and successful exploitation can interrupt the service.
The record
- CVE
- CVE-2026-91990
- Published
- Sep 15, 2026
- Updated
- Sep 15, 2026
- Vendor
- tornadoweb
- Product
- Tornado
- Classifications
- CWE-770, T1499.003
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 15, 2026CVE publishedPublication date reported by the CVE source.
- Sep 15, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <6.5.8
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Multipart memory-amplification PoCproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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