Service interruption via synchronous file rollover
Published Jul 21, 2025 · Updated Jul 22, 2025
Denial of service in Starlette before 0.47.2 allows remote attackers to block new connections by uploading a large multipart file. UploadFile.write checks only whether the spool is currently in memory, so a write crossing the size threshold performs disk rollover synchronously on the event-loop thread. An application must expose multipart form parsing; the demonstrated consequence is delayed or refused connections while rollover work blocks that thread.
Summary
What happened
Denial of service in Starlette before 0.47.2 allows remote attackers to block new connections by uploading a large multipart file. UploadFile.write checks only whether the spool is currently in memory, so a write crossing the size threshold performs disk rollover synchronously on the event-loop thread. An application must expose multipart form parsing; the demonstrated consequence is delayed or refused connections while rollover work blocks that thread.
The record
- CVE
- CVE-2025-54121
- Published
- Jul 21, 2025
- Updated
- Jul 22, 2025
- Vendor
- Kludex
- Product
- Starlette
- Classifications
- CWE-770, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 21, 2025CVE publishedPublication date reported by the CVE source.
- Jul 22, 2025Record 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=< 0.47.2
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 rollover reproductionproof 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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