CVE-2026-53538
CVE-2026-53538 is a low-severity vulnerability in Fastapiexpert Python-multipart with a CVSS 3.x base score of 3.7. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-436.
Key facts
- Severity: Low (CVSS 3.x base score 3.7)
- EPSS exploit prediction: 0% (7th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2026-38323
- Weakness: CWE-436
- Affected product: Fastapiexpert Python-multipart
- Published:
- Last modified:
Description
Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, QuerystringParser treated ; as a field separator in application/x-www-form-urlencoded bodies, in addition to &. The WHATWG URL standard, modern browsers, and Python's urllib.parse (since the CVE-2021-23336 fix) treat only & as a separator. This creates a parser differential: the same bytes are tokenized into different fields than a WHATWG compliant intermediary would produce, allowing an attacker to smuggle extra form fields past an upstream body inspecting component. This vulnerability is fixed in 0.0.30.
Frequently asked questions
- What is CVE-2026-53538?
- Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, QuerystringParser treated ; as a field separator in application/x-www-form-urlencoded bodies, in addition to &. The WHATWG URL standard, modern browsers, and Python's urllib.parse (since the CVE-2021-23336 fix) treat only & as a separator. This creates a parser differential: the same bytes are tokenized into different fields than a WHATWG compliant intermediary would produce, allowing an attacker to smuggle extra form fields past an upstream body inspecting component. This vulnerability is fixed in 0.0.30.
- How severe is CVE-2026-53538?
- CVE-2026-53538 has a CVSS 3.x base score of 3.7, rated low severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity low, and availability none.
- Is CVE-2026-53538 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (7th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2026-53538?
- CVE-2026-53538 affects Fastapiexpert Python-multipart. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2026-53538?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
- Does CVE-2026-53538 have an EU (EUVD) identifier?
- Yes. CVE-2026-53538 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-38323.
- When was CVE-2026-53538 published?
- CVE-2026-53538 was published on 2026-06-22 and last updated on 2026-06-26.
References
Affected products (1)
- cpe:2.3:a:fastapiexpert:python-multipart:*:*:*:*:*:python:*:*
More vulnerabilities in Fastapiexpert Python-multipart
- CVE-2026-24486 — High (CVSS 8.6): Python-Multipart is a streaming multipart parser for Python. Prior to version 0.0.22, a Path Traversal vulnerability…
- CVE-2026-53539 — High (CVSS 7.5): Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, when parsing…
- CVE-2024-24762 — High (CVSS 7.5): `python-multipart` is a streaming multipart parser for Python. When using form data, `python-multipart` uses a Regular…
- CVE-2026-40347 — Medium (CVSS 5.3): Python-Multipart is a streaming multipart parser for Python. Versions prior to 0.0.26 have a denial of service…
- CVE-2026-53540 — Low (CVSS 3.7): Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.31, parse_form() did not validate the…
- CVE-2026-53537 — Low (CVSS 3.7): Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.30, parse_options_header parsed…
All CVEs affecting Fastapiexpert Python-multipart →
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