CVE-2026-28356 | ReDoS in multipart 1.3.0 - `parse_options_header()`

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 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.

Published: 2026-03-12 Last update: 2026-04-16 Assigner: [email protected] Source: [email protected]
NVD Status：Deferred，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-28356 is rated Moderate Risk (56.4/100): CVSS High severity, with medium exploitation likelihood (EPSS 0.86%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-28356

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-19 0.82% 0.86% +0.04%
2 2026-04-13 0.71% 0.82% +0.11%
3 2026-03-18 — 0.71% —

Full EPSS history (4 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-28356

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]

Weakness enumeration for CVE-2026-28356

GitHub Security Advisory for CVE-2026-28356

GHSA-p2m9-wcp5-6qw3 · Severity: high · Ecosystem: pip — multipart vulnerable to ReDoS in `parse_options_header()`

OS Trackers for CVE-2026-28356

vendor priority summary link
debian not yet assigned CVE-2026-28356 not yet assigned priority: Debian including 1 source packages (multipart), 3 status rows across 3 suites (forky, sid, trixie): resolved 3. https://security-tracker.debian.org/tracker/CVE-2026-28356
redhat high — https://access.redhat.com/security/cve/CVE-2026-28356
ubuntu medium CVE-2026-28356 medium priority: Ubuntu including 1 source packages (multipart), 4 status rows across 4 suites (jammy, noble, questing, upstream): DNE 2, needs-triage 1, released 1. https://ubuntu.com/security/CVE-2026-28356

Affected software / configurations for CVE-2026-28356

Vendor Product Version Raw CPE
No affected products in dataset.

References for CVE-2026-28356

cvelogic Threat Intelligence