CVE-2026-55803 Overview
CVE-2026-55803 is an object injection vulnerability affecting Drupal core. The flaw stems from improperly controlled modification of dynamically-determined object attributes [CWE-915], enabling authenticated attackers with high privileges to manipulate object properties in ways developers did not intend. Successful exploitation can compromise confidentiality and integrity of the affected Drupal site.
The vulnerability affects multiple Drupal core branches, including 10.5.x, 10.6.x, 11.0.x, 11.1.x, 11.2.x, and 11.3.x. Drupal published advisory SA-CORE-2026-005 addressing the issue.
Critical Impact
Authenticated attackers with elevated privileges can inject object attributes to alter application logic, leading to high impact on data confidentiality and integrity across Drupal core installations.
Affected Products
- Drupal core versions 0.0.0 through 10.5.12
- Drupal core versions 10.6.0 through 10.6.11
- Drupal core versions 11.2.0 through 11.2.14, and 11.3.0 through 11.3.12
- Drupal core branches 11.0.* and 11.1.* (all releases)
Discovery Timeline
- 2026-07-10 - CVE-2026-55803 published to NVD
- 2026-07-16 - Last updated in NVD database
Technical Details for CVE-2026-55803
Vulnerability Analysis
CVE-2026-55803 is classified under CWE-915: Improperly Controlled Modification of Dynamically-Determined Object Attributes. This category of object injection occurs when application code assigns attributes to an object using attacker-controllable keys without validating which properties may be safely modified.
In Drupal core, this pattern typically appears when request data is mapped onto internal PHP objects or entity fields. When an attacker can influence the attribute name being assigned, they can overwrite properties that govern access control, serialization behavior, or downstream processing logic.
The attack requires network access and high privileges, but no user interaction. Exploitation complexity is high, indicating that specific preconditions or object states must be met for a successful attack.
Root Cause
The root cause lies in Drupal core code paths that iterate over user-supplied input and dynamically assign values to object attributes without an allowlist of permitted properties. This mass-assignment style pattern permits an authenticated user to reach and modify sensitive fields that were never intended to be user-writable.
Attack Vector
An attacker with an authenticated high-privileged Drupal account submits crafted input through a network-facing endpoint. The payload includes attribute names chosen to overwrite sensitive object properties during deserialization or entity hydration. Depending on which property is overwritten, downstream logic may execute using attacker-controlled state.
No verified public exploit or proof-of-concept has been published for CVE-2026-55803 at the time of writing. Refer to the Drupal Security Advisory SA-CORE-2026-005 for vendor technical details.
Detection Methods for CVE-2026-55803
Indicators of Compromise
- Unexpected modifications to Drupal entity or configuration objects performed by high-privileged accounts.
- Web server logs showing POST or PATCH requests to Drupal endpoints containing unusual property or attribute keys in the payload.
- Entries in Drupal watchdog logs referencing type errors, unexpected property assignments, or serialization warnings.
Detection Strategies
- Audit web application logs for administrative or privileged sessions submitting payloads with structurally unusual field names.
- Correlate authenticated privileged actions with subsequent changes to permissions, roles, or content entities that were not expected in the change management workflow.
- Deploy Web Application Firewall rules that inspect JSON and form-encoded bodies for object property keys matching internal Drupal class attributes.
Monitoring Recommendations
- Enable and centralize Drupal dblog or syslog output to a SIEM for correlation with authentication events.
- Track integrity of Drupal core files and configuration exports to detect unauthorized modifications post-exploitation.
- Alert on privilege escalation events, particularly changes to the administrator role membership or permission grants.
How to Mitigate CVE-2026-55803
Immediate Actions Required
- Upgrade Drupal core to a patched release listed in SA-CORE-2026-005 as soon as possible.
- Review accounts holding privileged roles and remove access from any account that does not require it.
- Rotate credentials and API keys for administrative accounts following the upgrade.
Patch Information
Drupal has issued fixed releases for the 10.5.x, 10.6.x, 11.2.x, and 11.3.x branches. Sites on unsupported branches such as 11.0.x and 11.1.x should migrate to a supported and patched version. Consult the vendor advisory at drupal.org/sa-core-2026-005 for exact fixed version numbers.
Workarounds
- Restrict administrative endpoints to trusted IP ranges via reverse proxy or firewall until the patch can be applied.
- Temporarily reduce the number of accounts assigned privileged roles to shrink the exploitable population.
- Enable strict input validation at the reverse proxy layer to block requests containing suspicious object attribute keys.
# Example: upgrade Drupal core using Composer
composer update drupal/core-recommended --with-dependencies
drush updatedb
drush cache:rebuild
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
