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CVE Record

CVE-2026-3427: Yoast SEO <= 27.1.1 - Authenticated (Contributor+) Stored Cross-Site Scripting via 'jsonText' Block Attribute

The Yoast SEO – Advanced SEO with real-time guidance and built-in AI plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the the `jsonText` block attribute in all versions up to, and including, 27.1.1 due to insufficient input sanitization and output escaping. This makes it possible for authenticated attackers, with Contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.

MediumCVSS 6.4Not KEV-listedUpdated
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Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

CVE-2026-3427 affects the Yoast SEO WordPress plugin through version 27.1.1. A logged-in user with Contributor or higher permissions can store malicious script in a Yoast-related block attribute. The script runs when someone views the affected page, creating risk to site users and administrators.

Executive priority

Treat as a timely plugin update and account-governance issue, not an emergency based on current evidence. Prioritize sites with many contributors, external authors, or high-value admin sessions. Complete remediation in the next normal WordPress maintenance window unless local indicators suggest abuse.

Technical view

The issue is stored cross-site scripting in the `jsonText` block attribute. Sources cite insufficient input sanitization and output escaping in Yoast SEO up to and including 27.1.1. CVSS 3.1 is 6.4, with low privileges required, network access, changed scope, and low confidentiality and integrity impact.

Likely exposure

WordPress sites running Yoast SEO versions up to and including 27.1.1 are potentially exposed, especially where Contributor-level accounts are allowed or compromised. Public self-registration, many authors, agencies, or weak account governance increase practical risk.

Exploitation context

No source in the bundle states active exploitation, and CISA KEV status is false. Exploitation requires authenticated Contributor-level or higher access. Impact depends on who views the injected page; stored XSS can affect visitors or privileged WordPress users.

Researcher notes

The vulnerability is tied to WordPress block data handling for `jsonText`, with references to Yoast code, a GitHub pull request, and WordPress.org changeset 3475308. The bundle does not provide public exploitation evidence or a detailed vendor advisory naming a fixed release.

Mitigation direction

  • Inventory WordPress sites using the Yoast SEO plugin.
  • Update Yoast SEO beyond 27.1.1 when a fixed release is available.
  • Review Yoast and WordPress plugin guidance for the confirmed fixed version.
  • Restrict Contributor and higher roles to trusted users only.
  • Remove unused author accounts and enforce strong authentication.
  • Review recent content changes by Contributor-level users.

Validation and detection

  • Check installed Yoast SEO versions across all WordPress sites.
  • Flag any Yoast SEO installation at 27.1.1 or earlier.
  • Confirm the installed build includes Yoast PR 23035 or changeset 3475308.
  • Review pages edited by Contributor-level users for unexpected scripts.
  • Verify Contributor users cannot publish unreviewed risky content.
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 · medium confidence lookup

CWE-79: User-session and phishing behavior lookup

Client-side and session-facing weaknesses should be reviewed alongside initial-access and user-execution behaviors. 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.

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cve · low confidence lookup

CVE-2026-3427 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
6.4 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

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.

1CVSS vectors
0Timeline events
0ADP providers
6Source links

CVSS vector scores

1 official score

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
6.4CVSS 3.1MediumCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N3.12.7Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

6.4Medium
CVSS 3.1 vector shape for CVE-2026-3427Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
yoastYoast SEO – Advanced SEO with real-time guidance and built-in AI0unaffected
Weakness

CWE details

CWE-79

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

CWE-79 · source CWE mapping

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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