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Full vulnerability report · 2026
CVE-2026-28356High confidence

ReDoS in multipart 1.3.0 - `parse_options_header()`

defnull · multipart

7.5HighCVSS 3.1
Recommended action
Within 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
Direct vendor intelligence

Authoritative vendor CSAF and VEX advisories

Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.

1 current
CVE-2026-28356 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitymultipart: denial of service via maliciously crafted HTTP or multipart segment headers
18 known affected

The vendor explicitly identifies these products as affected by this CVE.

  • lightspeed-core/lightspeed-stack-rhel9 as a component of Lightspeed Core
  • lightspeed-core/rag-tool-rhel9 as a component of Lightspeed Core
  • openshift-lightspeed/lightspeed-service-api-rhel9 as a component of OpenShift Lightspeed
  • rhaiis/vllm-cpu-rhel9 as a component of Red Hat AI Inference Server
  • rhaiis/vllm-neuron-rhel9 as a component of Red Hat AI Inference Server
  • rhaiis/vllm-spyre-rhel9 as a component of Red Hat AI Inference Server
  • rhaiis/vllm-tpu-rhel9 as a component of Red Hat AI Inference Server
  • rhelai3/bootc-aws-cuda-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3
  • rhelai3/bootc-azure-cuda-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3
  • rhelai3/bootc-azure-rocm-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3
  • rhelai3/bootc-cuda-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3
  • rhelai3/bootc-gcp-cuda-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3
Summary
A flaw was found in multipart. The parse_options_header function in multipart.py uses a regular expression with an ambiguous alternation, causing an exponential backtracking (ReDoS) when parsing a specially crafted HTTP or multipart segment headers. A web application parsing request headers or multipart/form-data streams can block request handling threads for multiple seconds per request, eventually resulting in a denial of service.
Remediation
For more information visit https://access.redhat.com/errata/RHSA-2026:6761
Optional official sources

National CERT insights
?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.

Select the national-authority views to include. The exact source language is shown on each matched advisory. Your choice is remembered on this device and encoded in the shareable URL.

Official European source

ENISA European Vulnerability Database

Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.

1 current
ENISA EUVD identifier

EUVD-2026-11607

No EUVD known-exploited evidence

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.

EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
7.5 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionWithin 7 days

High technical severity; prioritise exposed affected systems while verifying vendor guidance.

Patch available
01

What, why and how

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.

What

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.

Why

The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.

What

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.

Why

The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.

How

An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may disrupt the affected service.

02

Exploit reality and attack path

CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.

Observed exploitation
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
No confirmed evidence

No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.

Public PoC / exploit material
?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.
None recorded

No exploit-tagged reference or CISA SSVC proof-of-concept state is currently recorded. Research may still exist outside the structured feeds.

Likely attack path
a network path → Inefficient Regular Expression Complexity → disrupt the affected service
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness
?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-1333 ↗

CWE-1333: Inefficient Regular Expression Complexity. The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.

CVSS vector
?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.

AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CNoneConfidentiality impact: No direct loss is represented by this metric.INoneIntegrity impact: No direct loss is represented by this metric.AHighAvailability impact: A successful attack can cause a major loss.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
NetworkUnauthenticatedDenial of serviceCWE-1333
A

Official authority intelligence

Only matched European and national findings are included. Language selectors and unavailable sources are omitted.

ENISA EUVD · EUVD-2026-11607Official EUVD mapping

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.

Official EUVD record
03

Patch and workaround

Operational remediation based on structured source evidence.

Status
?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Patch available
Affected
lightspeed-core/lightspeed-stack-rhel9 as a component of Lightspeed Core; lightspeed-core/rag-tool-rhel9 as a component of Lightspeed Core; openshift-lightspeed/lightspeed-service-api-rhel9 as a component of OpenShift Lightspeed; rhaiis/vllm-cpu-rhel9 as a component of Red Hat AI Inference Server; rhaiis/vllm-neuron-rhel9 as a component of Red Hat AI Inference Server; rhaiis/vllm-spyre-rhel9 as a component of Red Hat AI Inference Server; rhaiis/vllm-tpu-rhel9 as a component of Red Hat AI Inference Server; rhelai3/bootc-aws-cuda-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3; rhelai3/bootc-azure-cuda-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3; rhelai3/bootc-azure-rocm-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3; rhelai3/bootc-cuda-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3; rhelai3/bootc-gcp-cuda-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3; rhelai3/bootc-rocm-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3; rhelai3/disk-image-cuda-rhel9 as a component of Red Hat Enterprise Linux AI (RHEL AI) 3; satellite/iop-advisor-engine-rhel9 as a component of Red Hat Satellite 6; satellite/iop-host-inventory-rhel9 as a component of Red Hat Satellite 6; satellite/iop-vmaas-rhel9 as a component of Red Hat Satellite 6; satellite/iop-vulnerability-engine-rhel9 as a component of Red Hat Satellite 6
Fixed
registry.redhat.io/rhaiis/model-opt-cuda-rhel9@sha256:950e0d72a64f8a7b6414be2d9ab01ba8342a900e3b4c272295a3d63ef0a6d22c_amd64 as a component of Red Hat AI Inference Server 3.2; registry.redhat.io/rhaiis/model-opt-cuda-rhel9@sha256:e2fc16946f33c8e701f4eff7fc5de9910df865051de0141114cebd3e2c10f0aa_arm64 as a component of Red Hat AI Inference Server 3.2; registry.redhat.io/rhaiis/vllm-cuda-rhel9@sha256:bd371b1b8785b2f5799cbca4a12a1c66a1e8a37017334a79eaa1067b24b6a6ba_amd64 as a component of Red Hat AI Inference Server 3.2; registry.redhat.io/rhaiis/vllm-cuda-rhel9@sha256:ee2846fae19a57151e878992484359bb834d91cada6b53c58e5c2a0b5675aa68_arm64 as a component of Red Hat AI Inference Server 3.2; registry.redhat.io/rhaiis/vllm-rocm-rhel9@sha256:3e9fbe1a078889d05d0291ef5cfba07924540609f8315c1c88d0f1a13eca5d45_amd64 as a component of Red Hat AI Inference Server 3.2; registry.redhat.io/rhoai/odh-caikit-tgis-serving-rhel9@sha256:7f45c61f9c5cf97867f60ac97a40df84fc76662252ed59c73da9b1f1670e7d72_amd64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-caikit-tgis-serving-rhel9@sha256:83ab708730c2450dfe7e64fe1165e407f188d4548d45acd7865ef2ec6aff8447_arm64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-feature-server-rhel9@sha256:0e355f088ca563163bc363f9b64b5ecbcacca919b724aab1cef4f9f218e9e775_arm64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-feature-server-rhel9@sha256:7c841a7b0be5bc5319300fd2a786a0c26698ea3ee4de524c4c2dd8f7da10d4ce_amd64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-feature-server-rhel9@sha256:e5d148e2bf1d88e746dfc4070499db92aff859986a15959e919ea262ca89e3d2_ppc64le as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-vllm-cpu-rhel9@sha256:0de336cd04325ccdb3c3ea4754f6f4da75f14829fb1e076cd1a917fa8a83a6d2_s390x as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-vllm-cpu-rhel9@sha256:c56430e69d1c4f3fbefc4c292318e69f02f486fcc63e138af06e3930ea23a7b5_ppc64le as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-vllm-cuda-rhel9@sha256:34fc1c2caaa4290d65e41ee75d30024b066f46b48e62d9f26c6f3cb0d3a78bae_arm64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-vllm-cuda-rhel9@sha256:d779464858681ad4e38b97e6465d9466a56f525c5d66164d577747ac8f4ab89e_amd64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-vllm-rocm-rhel9@sha256:55cae4fc505d942c4e32179da894dddf18627fbb74262cd0e7e42c7cfa54508d_amd64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-vllm-cpu-rhel9@sha256:a5dc659cd3af310c063f2734ddfba749b58a2a1366c983b2fbd677ed8cd97100_s390x as a component of Red Hat OpenShift AI 3.3; registry.redhat.io/rhoai/odh-vllm-cpu-rhel9@sha256:b01237af8596f00232670e1d49d76832f22095c6f3febc8b0b9934325320608a_ppc64le as a component of Red Hat OpenShift AI 3.3
Action
For more information visit https://access.redhat.com/errata/RHSA-2026:6761
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04

Evidence and provenance

Published 12 Mar 2026 · Last source change 24 Aug 2026, 12:07 UTC · CWE-1333 · Inefficient Regular Expression Complexity

CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source
?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.
FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-11607
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD not scheduled

Core structured fields are present and their contributing authorities are shown above.

Material change intelligence

What changed after publication

View recent updates →

No material field changes have been recorded since change tracking began. Routine source refreshes and cosmetic edits are intentionally excluded.

Material fields only · duplicate refreshes suppressed · history retained for the configured operational retention period
CVE published
ENISA EUVD · EUVD-2026-11607↗Vendor CSAF · Red Hat Product Security↗CVE authority or vendor reference↗Official CVE record (CNA and ADP data)↗NVD record↗
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.
Free version - for non-commercial use only.CVE-2026-28356 · cve.blacktree.nl