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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

A flaw in the Python multipart library can let an unauthenticated remote attacker consume excessive processing time with malicious request headers. Applications using affected versions to parse HTTP headers or multipart uploads may become slow or unavailable. The documented impact is denial of service, not data theft or modification.

Executive priority

High priority for public-facing applications because a remote unauthenticated request may impair availability. Patch reachable upload and form-processing services promptly, then address internal deployments according to business criticality. No confidentiality or integrity impact, active exploitation, or KEV inclusion is established by the supplied evidence.

Technical view

The parse_options_header() function contains a regular expression with ambiguous alternation, allowing exponential backtracking on crafted HTTP or multipart segment headers. Affected releases are versions below 1.2.2 and versions 1.3.0 through 1.3.0. Fixes are identified in 1.2.2, 1.3.1, and 1.4.0-dev. CVSS 3.1 is 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H).

Likely exposure

Exposure is highest for internet-accessible Python applications that use affected multipart versions and pass attacker-controlled HTTP or multipart headers to parse_options_header(). Installation alone does not prove reachability. Internal services and applications that do not process untrusted multipart or header input have lower practical exposure.

Exploitation context

The CVSS assessment indicates remote, low-complexity, unauthenticated exploitation requiring no user interaction. The source bundle reports no CISA KEV listing and provides no evidence of active exploitation. Treat exploit prevalence as unknown while prioritizing externally reachable upload and form-processing services.

Researcher notes

CWE-1333 applies to inefficient regular-expression complexity. Practical risk depends on vulnerable-version presence and whether attacker-controlled header values reach parse_options_header(). The bundle identifies upstream fixes and several Red Hat advisories, but does not establish affected framework integrations, observed attacks, or exploitation at scale. Avoid inferring exposure solely from package installation.

Mitigation direction

  • Upgrade affected installations to multipart 1.2.2 or 1.3.1, following the maintained dependency branch.
  • Review vendor guidance before using the 1.4.0-dev fix in production.
  • Apply applicable Red Hat errata when multipart is supplied through supported Red Hat products.
  • Prioritize internet-facing services that parse uploads, forms, or attacker-controlled request headers.
  • Use existing request limits and traffic controls to reduce denial-of-service exposure until upgrades complete.

Validation and detection

  • Inventory installed and transitive multipart versions using lockfiles, SBOMs, and deployment artifacts.
  • Confirm whether untrusted headers can reach parse_options_header() in each affected application.
  • Verify production instances run 1.2.2, 1.3.1, or a vendor-fixed package.
  • Regression-test legitimate multipart uploads and header parsing after remediation.
  • Monitor affected services for unusual CPU saturation, latency, and repeated malformed-request patterns.
Prepared
Confidence
high
Sources
6

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
11Source 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

Inefficient Regular Expression Complexity

Inefficient Regular Expression Complexity represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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