Vulnerability in Drupal core (CVE-2026-55803)
Summary
Vulnerability in Drupal core (CVE-2026-55803). Confidential information can be exposed externally.
Original description
The description as published by the source.
SA-CORE-2019-003 added protection for fields that store serialized data to disallow direct writes via web services.
The above fix did not cover all potential attack vectors for JSON:API. An attacker with appropriate JSON:API write permission could potentially inject a malicious payload in certain rare circumstances, potentially resulting in PHP Object Injection.
This vulnerability is mitigated by the fact that in order to be exploitable:
- A site must use an entity reference field type that stores a serialized property.
- An attacker must have permission to write to the entity via JSON:API.
No field type shipped with Drupal core meets these criteria, and contributed or user-created field types that do appear to be extremely unusual. This update protects all such fields; no changes are required in contributed modules.
JSON:API is read-only by default, so sites are only affected if they have enabled write access (either through administrator configuration or the installation of a contributed or custom module that enables write access).
Drupal Steward protection:
This issue is being protected by Drupal Steward. In this instance, we believe that the WAF rule will provide mitigation for the common/obvious vulnerability paths, but may not cover all cases or work for all hosting providers. Additionally, several other core security advisories released today are not mitigated by Drupal Steward.…
Source: NIST National Vulnerability Database NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-55803 has been found in Drupal core.
Confidential information can be exposed externally. CVSS score: 5.9/10.
What to do: apply the vendor's official patched release.
If unsure, ask your IT team or search "Drupal core CVE-2026-55803" on the vendor's site.
CVE-2026-55803 (Drupal core) — CWE-915 / CVSS v3 5.9
Attack vector: remote (network-reachable) / no user interaction
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
A vulnerability (CWE-915) exists in Drupal core.
Check the vendor advisory for the affected versions of Drupal core.
Severity: Medium (CVSS 5.9/10). Confidential information can be exposed externally.
Update to the patched release per vendor advisory.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Audit SBOM/dependencies to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
Audit SBOM/dependencies for affected components.資産台帳・SBOM・依存マニフェストで Drupal core を使っているサービスとバージョンを洗い出す。
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2Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
References
- web drupal.org
- web nvd.nist.gov
- web github.com