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CVE Record

CVE-2026-42561: Python-Multipart: Denial of Service via unbounded multipart part headers

Python-Multipart is a streaming multipart parser for Python. Prior to 0.0.27, python-multipart has a denial of service vulnerability in multipart part header parsing. When parsing multipart/form-data, MultipartParser previously had no limit on the number of part headers or the size of an individual part header. An attacker could send a request with either many repeated headers without terminating the header block or a single very large header value, causing excessive CPU work before request rejection or completion. This vulnerability is fixed in 0.0.27.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2026-42561 lets a remote attacker waste server CPU by sending specially shaped multipart form uploads to software using python-multipart before 0.0.27. The issue affects availability, not data confidentiality or integrity. The public sources state it is fixed in python-multipart 0.0.27.

Executive priority

Treat this as a high-priority availability fix for services accepting uploads or multipart forms. Prioritize public-facing and high-traffic systems first. The main business risk is service degradation or outage, not confirmed data theft.

Technical view

Before 0.0.27, python-multipart did not limit multipart part header count or individual part header size. During multipart/form-data parsing, excessive repeated headers or a very large header value could cause heavy CPU work before rejection or completion. CVSS 3.1 is 7.5: network, low complexity, unauthenticated, availability impact only.

Likely exposure

Exposure is likely where internet-facing or internal services parse untrusted multipart/form-data using python-multipart versions earlier than 0.0.27, directly or through dependencies. File upload and form submission paths deserve priority review.

Exploitation context

The source bundle marks KEV as false, and no cited source states active exploitation. The attack does not require authentication or user interaction according to the CVSS vector, but public evidence here only supports denial-of-service risk, not data compromise.

Researcher notes

The weakness maps to unbounded resource consumption during header parsing, with CWE-606 and CWE-770 cited. Evidence supports vulnerable versions below 0.0.27 and a fixed upstream release. No exploit telemetry, proof-of-concept status, or broad product impact is provided in the supplied bundle.

Mitigation direction

  • Upgrade python-multipart to 0.0.27 or later.
  • Identify and update transitive dependencies that package vulnerable python-multipart versions.
  • For Red Hat environments, follow RHSA-2026:37275 and related Red Hat guidance.
  • Check vendor advisories for product-specific backports or mitigations.

Validation and detection

  • Inventory deployed python-multipart versions across applications and images.
  • Confirm multipart/form-data parsing paths use python-multipart 0.0.27 or later.
  • Review dependency lockfiles and SBOMs for python-multipart versions below 0.0.27.
  • Verify Red Hat package status against the referenced errata where applicable.
Prepared
Confidence
high
Sources
7

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

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · low confidence lookup

CWE-606: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cwe · low confidence lookup

CWE-770: Exact CWE lookup

Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-42561 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
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
6Source 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-2026-42561Attack 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-SADPpython-multipart: python-multipart: Denial of Service via excessive multipart part headers
other:Red Hat severity ratingcvssV3_1
  • 2026-05-13T22:01:05.319Z: Reported to Red Hat.
  • 2026-05-13T20:55:11.767Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Kludexpython-multipart< 0.0.27Listed
Weakness

CWE details

CWE-606CWE-770

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

CWE-606 · source CWE mapping

Unchecked Input for Loop Condition

Unchecked Input for Loop Condition represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs
CWE-770 · source CWE mapping

Allocation of Resources Without Limits or Throttling

Allocation of Resources Without Limits or Throttling represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs