PatchSiren

PatchSiren cyber security CVE debrief

CVE-2026-42556 Gitroom CVE debrief

Postiz versions 2.21.6 through 2.21.6 (before 2.21.7) contain a stored cross-site scripting vulnerability. Authenticated users with post creation privileges can inject arbitrary HTML into post content by tampering with save requests. This HTML is rendered unsafely via dangerouslySetInnerHTML on public preview pages at /p/<postId>?share=true, enabling attacks against viewers of shared post previews. The vulnerability was patched in version 2.21.7.

Vendor
Gitroom
Product
Postiz
CVSS
HIGH 8.9
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-08
Original CVE updated
2026-07-24
Advisory published
2026-05-08
Advisory updated
2026-07-24

Who should care

Organizations running self-hosted Postiz instances; security teams monitoring social media management platforms; developers using React applications with dangerouslySetInnerHTML

Technical summary

The vulnerability exists in Postiz's post creation flow where client-side request tampering allows authenticated users to bypass content sanitization and store arbitrary HTML. The public preview endpoint /p/<postId>?share=true renders this content using React's dangerouslySetInnerHTML prop without adequate sanitization, executing attacker-controlled scripts in the context of the main application origin. This creates a stored XSS condition exploitable through social engineering distribution of preview links.

Defensive priority

HIGH

Recommended defensive actions

  • Upgrade Postiz to version 2.21.7 or later
  • Review application logs for suspicious post content containing script tags or event handlers in the disclosure-to-patch window
  • Implement Content Security Policy headers to mitigate impact of any residual XSS vectors
  • Audit user accounts with post creation privileges for anomalous activity
  • Consider input sanitization layers for post content regardless of client-side validation

Evidence notes

NVD analyzed status; GitHub Security Advisory GHSA-hhxq-3wg7-4rj8; vendor release notes confirm patch in v2.21.7. CVSS 3.1 vector: AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:L. CWE-79 classification.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-42556 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-42556

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-42556 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-42556

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.