Security readout for executives and security teams
Plain-English summary
This flaw can let an unauthenticated remote attacker make affected Rack-based Ruby applications consume excessive CPU while parsing specially formed multipart form requests. The likely business impact is service degradation or outage on applications that accept multipart form data, such as upload or form submission endpoints.
Executive priority
Treat as a high-priority availability risk for affected public Ruby applications. Patch exposed multipart-handling services promptly, with greatest urgency for unauthenticated upload or form endpoints supporting customer-facing operations.
Technical view
Rack::Multipart::Parser#handle_mime_head in affected Rack versions performs repeated string searches and prefix deletions while parsing quoted multipart parameters. Escape-heavy quoted values can trigger super-linear processing, causing algorithmic-complexity denial of service during multipart/form-data parsing.
Likely exposure
Exposure is most likely in Ruby applications using Rack versions 3.0.0.beta1 through before 3.1.21, or 3.2.0 through before 3.2.6, where the application accepts multipart/form-data requests. Internet-facing, unauthenticated upload or form endpoints are higher priority.
Exploitation context
The source bundle does not show KEV listing or cited evidence of active exploitation. The described attack is network reachable, low complexity, unauthenticated, and affects availability, not confidentiality or integrity.
Researcher notes
The key condition is parser reachability, not just dependency presence. Validate the exact Rack version loaded at runtime and whether multipart parsing occurs before authentication or request rejection. Evidence provided supports patched versions but does not establish active exploitation.
Mitigation direction
- Upgrade Rack to 3.1.21, 3.2.6, or later patched versions.
- Redeploy all services bundling an affected Rack version.
- Prioritize internet-facing applications accepting multipart/form-data.
- Check Rack and downstream vendor guidance for supported temporary controls.
- Confirm dependency locks and container images no longer include affected versions.
Validation and detection
- Inventory Ruby services and dependency lockfiles for Rack versions.
- Identify routes accepting multipart/form-data, especially unauthenticated endpoints.
- Verify production artifacts use Rack 3.1.21, 3.2.6, or later.
- Review edge and application logs for unusual multipart request volume.
- Run regression tests for upload and form submission workflows after upgrading.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
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-400: Exact CWE lookup
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Open ATT&CK lookupCWE-407: 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 lookupCWE-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 lookupCVE-2026-34827 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- 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
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.
SSVC decision data
CVSS vector scores
2 official scoresWe 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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6GitHub_MCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6redhat-SADPVulnerability scoring details
Base CVSS 3.1 score
7.5HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Base CVSS 3.1 score
7.5HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- ADP timelineredhat-SADP
Made public.
- CVE publishedCVE Program
The CVE record was published.
- ADP timelineredhat-SADP
Reported to Red Hat.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
- 2026-04-02T18:02:05.760Z: Reported to Red Hat.
- 2026-04-02T17:07:48.279Z: Made public.
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/rack/rack/security/advisories/GHSA-v6x5-cg8r-vv6xCVE reference, GitHub_M · x_refsource_CONFIRM
- https://access.redhat.com/security/cve/CVE-2026-34827CVE reference, redhat-SADP · vdb-entry, x_refsource_REDHAT
- RHBZ#2454501CVE reference, redhat-SADP · issue-tracking, x_refsource_REDHAT
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34827.jsonCVE reference, redhat-SADP · x_sadp-csaf-vex
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Uncontrolled Resource Consumption
Uncontrolled Resource Consumption represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Inefficient Algorithmic Complexity
Inefficient Algorithmic Complexity represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
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.