vulnerability / NVI-00018467 / Revision 1
python-multipart: Quadratic-time querystring parsing with semicolon separators causes CPU denial of service
GitHub lists this reviewed advisory for python-multipart. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
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7.5 high
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
python-multipart
source listed< 0.0.30
### Summary 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. ### Details In `python_multipart/multipart.py`, both the `FIELD_NAME` and `FIELD_DATA` states located the next separator like this: ```python sep_pos = data.find(b"&", i) if sep_pos == -1: sep_pos = data.find(b";", i) ``` `data.find(b"&", i)` scans from `i` to the end of the buffer and returns `-1` only when there is no `&` anywhere in the remainder. For a `;` separated body with no `&`, this failed full buffer scan repeats once per f
03 / Response
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- investigate
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04 / Limits
What this report cannot establish
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05 / Provenance
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- GHSA-5rvq-cxj2-64vf ↗
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- Revision 1 ·
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