Unauthenticated server crash via empty multipart field
Published Jul 27, 2026 · Updated Jul 27, 2026
Integer underflow in facil.io 0.6.0 through 0.7.6 allows remote attackers to crash the server via a crafted multipart POST request. In http_mime_parser.h, an empty Content-Disposition name leaves name_len at zero before name[name_len - 1] wraps and reads out of bounds. Network reachability to an application using the multipart parser is required; one request kills a worker, while a single-worker server goes offline.
Summary
What happened
Integer underflow in facil.io 0.6.0 through 0.7.6 allows remote attackers to crash the server via a crafted multipart POST request. In http_mime_parser.h, an empty Content-Disposition name leaves name_len at zero before name[name_len - 1] wraps and reads out of bounds. Network reachability to an application using the multipart parser is required; one request kills a worker, while a single-worker server goes offline.
The record
- CVE
- CVE-2026-66729
- Published
- Jul 27, 2026
- Updated
- Jul 27, 2026
- Vendor
- Boaz Segev
- Product
- facil.io
- Classifications
- CWE-125, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 27, 2026CVE publishedPublication date reported by the CVE source.
- Jul 27, 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=0.6.0 <=0.7.6
What conditions does exploitation require?
What is affected?
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.
Public exploit references
- CVE-2026-66729.py multipart crash proof of conceptproof of concept · demonstrated
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Technologies
Your stack
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Your stack
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