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CVE Record

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.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2026-28356 is a denial-of-service flaw in the Python multipart library. A maliciously crafted HTTP or multipart header can make vulnerable applications spend excessive CPU while parsing, potentially making upload or form-handling services unavailable. The sources describe availability impact only, not data theft or data modification.

Executive priority

Treat this as a high-priority availability risk for exposed web services using multipart. Patch promptly where the library is present, especially on externally reachable systems, but do not classify it as known exploited based on the supplied sources.

Technical view

The vulnerable parse_options_header() function in multipart.py uses a regular expression with ambiguous alternation, enabling exponential backtracking. Affected versions are defnull multipart before 1.2.2 and 1.3.0 before 1.3.1. Fixed versions are listed as 1.2.2, 1.3.1, and 1.4.0-dev.

Likely exposure

Exposure is most likely in Python web applications or services that use defnull multipart to parse HTTP headers or multipart/form-data streams, especially public upload, form submission, or API endpoints.

Exploitation context

The CVSS vector indicates network reachability, low attack complexity, no privileges, and no user interaction. The bundle does not show CISA KEV listing or other cited evidence of active exploitation.

Researcher notes

The record maps to CWE-1333 and CVSS 3.1 score 7.5. Evidence identifies a regex ReDoS in parse_options_header(), but the bundle does not include proof-of-concept details, observed exploitation, or a complete downstream product list.

Mitigation direction

  • Upgrade multipart to 1.2.2, 1.3.1, or a fixed later release.
  • Inventory Python services that parse multipart/form-data or request headers.
  • Check Red Hat advisories for distribution-specific package status.
  • Apply vendor guidance where bundled or transitive dependencies are involved.
  • Use request size and timeout controls as defense-in-depth.

Validation and detection

  • Check dependency manifests and lockfiles for defnull multipart versions.
  • Confirm runtime environments do not load affected multipart versions.
  • Prioritize internet-facing upload, form, and API endpoints for review.
  • Verify patched package versions in built containers and deployed hosts.
  • Review logs and metrics for unexplained CPU spikes during header parsing.
Prepared
Confidence
high
Sources
11

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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cwe · low confidence lookup

CWE-1333: Exact CWE lookup

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cve · low confidence lookup

CVE-2026-28356 mapping review

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Vulnerability profileCVE Program record
Severity
High
CVSS
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
10Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: yesTechnical Impact: partial

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6GitHub_M
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-28356Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPmultipart: denial of service via maliciously crafted HTTP or multipart segment headers
other:Red Hat severity ratingcvssV3_1
  • 2026-03-12T18:01:57.290Z: Reported to Red Hat.
  • 2026-03-12T16:45:01.070Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
defnullmultipart>= 1.3.0, < 1.3.1, < 1.2.2Listed
Weakness

CWE details

CWE-1333

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-1333 · source CWE mapping

CWE mapping pending import

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