CVE-2026-53539: CWE-400: Uncontrolled Resource Consumption in Kludex python-multipart
Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, when parsing application/x-www-form-urlencoded bodies, QuerystringParser located the field separator with a two step lookup: it first scanned the entire remaining buffer for &, and only when no & existed anywhere ahead did it fall back to scanning for ;. For a body that uses ; as the separator and contains no &, every field iteration performed a full failed & scan over the entire remaining buffer before locating the nearby ;. With N semicolon separated fields in a chunk of size B, this yields O(B^2) byte comparisons per chunk. An attacker can submit a small crafted body of the form a;a;a;... and cause the parser to spend seconds of CPU per request. A handful of concurrent requests can exhaust worker processes. This vulnerability is fixed in 0.0.30.
AI Analysis
Technical Summary
The python-multipart library versions before 0.0.30 contain a performance flaw in the QuerystringParser when parsing application/x-www-form-urlencoded bodies that use semicolon (;) as field separators without ampersands (&). The parser performs a full scan for '&' on each field iteration before falling back to scanning for ';', resulting in O(B^2) byte comparisons for a chunk of size B with N semicolon-separated fields. This inefficiency can be exploited by an attacker sending crafted bodies like 'a;a;a;...' to cause excessive CPU usage and potentially exhaust worker processes. The issue is addressed in version 0.0.30.
Potential Impact
The vulnerability causes high CPU consumption leading to denial of service conditions by exhausting worker processes handling requests. It does not impact confidentiality or integrity but affects availability due to resource exhaustion.
Mitigation Recommendations
Upgrade python-multipart to version 0.0.30 or later where this vulnerability is fixed. Patch status is confirmed by the vendor's versioning. No other mitigations are indicated.
CVE-2026-53539: CWE-400: Uncontrolled Resource Consumption in Kludex python-multipart
Description
Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, when parsing application/x-www-form-urlencoded bodies, QuerystringParser located the field separator with a two step lookup: it first scanned the entire remaining buffer for &, and only when no & existed anywhere ahead did it fall back to scanning for ;. For a body that uses ; as the separator and contains no &, every field iteration performed a full failed & scan over the entire remaining buffer before locating the nearby ;. With N semicolon separated fields in a chunk of size B, this yields O(B^2) byte comparisons per chunk. An attacker can submit a small crafted body of the form a;a;a;... and cause the parser to spend seconds of CPU per request. A handful of concurrent requests can exhaust worker processes. This vulnerability is fixed in 0.0.30.
CVSS v3.1
Score 7.5high
Affected software
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AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The python-multipart library versions before 0.0.30 contain a performance flaw in the QuerystringParser when parsing application/x-www-form-urlencoded bodies that use semicolon (;) as field separators without ampersands (&). The parser performs a full scan for '&' on each field iteration before falling back to scanning for ';', resulting in O(B^2) byte comparisons for a chunk of size B with N semicolon-separated fields. This inefficiency can be exploited by an attacker sending crafted bodies like 'a;a;a;...' to cause excessive CPU usage and potentially exhaust worker processes. The issue is addressed in version 0.0.30.
Potential Impact
The vulnerability causes high CPU consumption leading to denial of service conditions by exhausting worker processes handling requests. It does not impact confidentiality or integrity but affects availability due to resource exhaustion.
Mitigation Recommendations
Upgrade python-multipart to version 0.0.30 or later where this vulnerability is fixed. Patch status is confirmed by the vendor's versioning. No other mitigations are indicated.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-06-09T18:13:07.263Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 6a39735aeed863c81e396233
Added to database: 06/22/2026, 17:39:38 UTC
Last enriched: 06/29/2026, 21:51:05 UTC
Last updated: 08/05/2026, 09:52:12 UTC
Views: 69
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