WAF bypass via NUL-truncated uploaded file content
Published Jan 20, 2023 · Updated Apr 2, 2025
Improper null termination in OWASP ModSecurity before 2.9.7 allows remote attackers to bypass WAF rules via crafted file uploads. The var_files_tmp_contents_generate function joins 1,023-byte fread chunks with NUL-terminated string formatting, so an embedded NUL truncates FILES_TMP_CONTENT while its recorded length can extend beyond the assembled buffer. Exposure requires multipart upload inspection and a rule that reads FILES_TMP_CONTENT; the content mismatch permits uninspected payload data and buffer over-reads in the WAF process.
Summary
What happened
Improper null termination in OWASP ModSecurity before 2.9.7 allows remote attackers to bypass WAF rules via crafted file uploads. The var_files_tmp_contents_generate function joins 1,023-byte fread chunks with NUL-terminated string formatting, so an embedded NUL truncates FILES_TMP_CONTENT while its recorded length can extend beyond the assembled buffer. Exposure requires multipart upload inspection and a rule that reads FILES_TMP_CONTENT; the content mismatch permits uninspected payload data and buffer over-reads in the WAF process.
The record
- CVE
- CVE-2023-24021
- Published
- Jan 20, 2023
- Updated
- Apr 2, 2025
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- CWE-170, T1562.001
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jan 20, 2023CVE publishedPublication date reported by the CVE source.
- Apr 2, 2025Record updatedLatest update available in the CVE record.
Exploitability
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Published CVSS scores
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Attacks
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Technologies
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Your stack
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