CVE-2026-28356
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2026-28356 is a high-severity Inefficient Regular Expression Complexity (CWE-1333) vulnerability in Redhat (inferred from references). Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Endpoint Denial of Service (T1499); ranked in the top 36% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-15 (Development Process, Standards, and Tools) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-28356 is a regular expression denial-of-service (ReDoS) vulnerability in the 'multipart' Python library, a fast parser for multipart/form-data. The issue affects the parse_options_header() function in multipart.py, which uses a regular expression with an ambiguous alternation that triggers exponential backtracking when processing maliciously crafted HTTP or multipart segment headers. It impacts versions prior to 1.2.2, 1.3.1, and 1.4.0-dev, earning a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) and mapping to CWE-1333 (Inefficient Regular Expression Complexity).
An unauthenticated attacker over the network can exploit this vulnerability by sending specially crafted HTTP requests or multipart/form-data streams containing headers designed to maximize backtracking in the regex engine. Successful exploitation causes excessive CPU consumption, leading to denial-of-service conditions in web applications that rely on the library for parsing such inputs, potentially rendering services unresponsive without requiring user interaction or privileges.
The GitHub security advisory at https://github.com/defnull/multipart/security/advisories/GHSA-p2m9-wcp5-6qw3 details the fix, which resolves the ReDoS issue in versions 1.2.2, 1.3.1, and 1.4.0-dev. Security practitioners should update affected applications to these patched releases and review dependencies using the 'multipart' library for vulnerable versions.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-11607
Vulnerability Data
multipart is a fast multipart/form-data parser for python. Prior to 1.2.2, 1.3.1 and 1.4.0-dev, the parse_options_header() function in multipart.py uses a regular expression with an ambiguous alternation, which can cause exponential backtracking (ReDoS) when parsing maliciously crafted HTTP or multipart…
more
segment headers. This can be abused for denial of service (DoS) attacks against web applications using this library to parse request headers or multipart/form-data streams. The issue is fixed in 1.2.2, 1.3.1 and 1.4.0-dev.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation can discover inefficient regex patterns via performance or static analysis.
Development standards and tools can require safe regex construction and forbid known exponential patterns.
Denial-of-service protections limit resource exhaustion caused by expensive regex evaluation.
Input validation can constrain data that would otherwise trigger worst-case regex complexity.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing can detect and reject regex patterns with exponential worst-case complexity.
Secure coding standards explicitly prohibit or limit the use of inefficient regular expressions.