Service interruption via multipart length underflow
Published Apr 23, 2026 · Updated Apr 23, 2026
Integer underflow in SWUpdate 2025.12 and earlier allows remote attackers to interrupt the update service via a crafted /upload request. In mg_http_multipart_continue_wait_for_chunk(), a +6 length guard precedes subtraction of the boundary length plus 8, underflowing data_len for two buffer lengths and causing an out-of-bounds heap read. The request requires no authentication but requires controlled TCP stream timing; successful exploitation makes the service unavailable.
Summary
What happened
Integer underflow in SWUpdate 2025.12 and earlier allows remote attackers to interrupt the update service via a crafted /upload request. In mg_http_multipart_continue_wait_for_chunk(), a +6 length guard precedes subtraction of the boundary length plus 8, underflowing data_len for two buffer lengths and causing an out-of-bounds heap read. The request requires no authentication but requires controlled TCP stream timing; successful exploitation makes the service unavailable.
The record
- CVE
- CVE-2026-28525
- Published
- Apr 23, 2026
- Updated
- Apr 23, 2026
- Vendor
- SWUpdate
- Product
- SWUpdate
- Classifications
- CWE-125, CWE-191, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 23, 2026CVE publishedPublication date reported by the CVE source.
- Apr 23, 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 <=2025.12
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.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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