Security readout for executives and security teams
Plain-English summary
Happy DOM, a server-side browser-like JavaScript library, could send cookies for the page origin to a different request destination during credentialed fetches. In affected versions, this creates a confidentiality risk: cookies intended for one origin may be exposed to another. The published fix is version 20.8.9.
Executive priority
Prioritize remediation where Happy DOM is used in automation, rendering, scraping, or test infrastructure that handles real cookies or secrets. For isolated test-only use with synthetic cookies, urgency is lower, but upgrading remains the cleanest control.
Technical view
Versions before 20.8.9 selected cookies from window.location rather than the target request URL for fetch with credentials include. The issue is classified as CWE-201 and CWE-359 with CVSS 7.5, network attack vector, low complexity, no privileges or user interaction, and high confidentiality impact only.
Likely exposure
Exposure is likely limited to applications, tests, crawlers, renderers, or tooling that use happy-dom versions below 20.8.9 and perform credentialed fetches with cookies present. The bundle identifies capricorn86 happy-dom as the affected product; no other products are listed.
Exploitation context
The source bundle does not identify active exploitation, and KEV is false. The risk is data leakage through incorrect cookie attachment, not code execution. Practical impact depends on whether sensitive cookies exist in Happy DOM sessions and whether credentialed cross-origin requests occur.
Researcher notes
The key flaw is origin confusion in cookie selection for credentialed fetches. Sources point to the advisory, pull request, commit, vulnerable utility file, and v20.8.9 release. Evidence supports the affected range and fix, but does not establish exploitation in the wild.
Mitigation direction
- Upgrade happy-dom to version 20.8.9 or later.
- Review lockfiles and transitive dependency paths for affected versions.
- Check vendor advisory and release notes before relying on alternate mitigations.
- Reduce credentialed cross-origin fetch use where it is not required.
- Treat exposed session cookies as potentially compromised if logs show risky flows.
Validation and detection
- Inventory package manifests and lockfiles for happy-dom below 20.8.9.
- Identify Happy DOM code paths using credentialed fetch with cookies present.
- Confirm resolved dependency version is 20.8.9 or later after update.
- Review tests or tooling that simulate multiple origins with shared cookie state.
- Check application logs for unexpected outbound requests carrying sensitive cookies.
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-201: Information exposure and cloud metadata lookup
Information exposure and SSRF weaknesses can make discovery, cloud metadata, and credential material review relevant. 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-359: 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-2026-34226 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:H/I:N/A:N
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:H/I:N/A:N3.93.6GitHub_MCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N3.93.6redhat-SADPVulnerability scoring details
Base CVSS 3.1 score
7.5HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Base CVSS 3.1 score
7.5HighVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
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
- 2026-03-27T22:02:34.704Z: Reported to Red Hat.
- 2026-03-27T21:17:24.777Z: Made public.
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/capricorn86/happy-dom/security/advisories/GHSA-w4gp-fjgq-3q4gCVE reference, GitHub_M · x_refsource_CONFIRM
- https://github.com/capricorn86/happy-dom/pull/2117CVE reference, GitHub_M · x_refsource_MISC
- https://github.com/capricorn86/happy-dom/commit/68324c21d7b98f53f7bb5a7b3e185bda7106e751CVE reference, GitHub_M · x_refsource_MISC
- https://github.com/capricorn86/happy-dom/blob/f8d8cad41e9722fab9eefb9dfb3cca696462e908/packages/happy-dom/src/fetch/utilities/FetchRequestHeaderUtility.tsCVE reference, GitHub_M · x_refsource_MISC
- https://github.com/capricorn86/happy-dom/releases/tag/v20.8.9CVE reference, GitHub_M · x_refsource_MISC
- https://access.redhat.com/security/cve/CVE-2026-34226CVE reference, redhat-SADP · vdb-entry, x_refsource_REDHAT
- RHBZ#2452519CVE reference, redhat-SADP · issue-tracking, x_refsource_REDHAT
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-34226.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.
Insertion of Sensitive Information Into Sent Data
Insertion of Sensitive Information Into Sent Data represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Exposure of Private Personal Information to an Unauthorized Actor
Exposure of Private Personal Information to an Unauthorized Actor represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.