CVE-2026-31821 Overview
CVE-2026-31821 is a Broken Access Control vulnerability affecting Sylius, an Open Source eCommerce Framework built on Symfony. The vulnerability exists in the POST /api/v2/shop/orders/{tokenValue}/items endpoint, which fails to verify cart ownership before allowing item additions. This allows unauthenticated attackers to manipulate other customers' shopping carts by knowing or obtaining their cart tokenValue.
Critical Impact
Attackers can add arbitrary items to registered customers' shopping carts without authentication, potentially leading to cart manipulation, customer confusion, inventory issues, and exposure of full cart details in API responses.
Affected Products
- Sylius versions prior to 2.0.16
- Sylius versions prior to 2.1.12
- Sylius versions prior to 2.2.3
Discovery Timeline
- 2026-03-10 - CVE-2026-31821 published to NVD
- 2026-03-11 - Last updated in NVD database
Technical Details for CVE-2026-31821
Vulnerability Analysis
This vulnerability is classified as CWE-862 (Missing Authorization). The core issue lies in the Sylius API's failure to implement proper ownership validation on cart manipulation endpoints. When processing requests to add items to a shopping cart, the API endpoint trusts the provided tokenValue parameter without verifying that the requesting user has legitimate access to that cart.
The attack is network-based and requires no privileges or user interaction. An attacker who obtains a valid cart tokenValue—through various means such as URL sharing, session token exposure, or brute-force enumeration—can directly manipulate that cart's contents. The API responds with HTTP 201 status and returns the complete cart representation, potentially exposing sensitive customer shopping data including item selections, quantities, and pricing information.
Root Cause
The root cause of this vulnerability is the absence of authorization checks in the POST /api/v2/shop/orders/{tokenValue}/items endpoint. The Sylius framework relies on cart token values as identifiers but does not validate whether the authenticated or anonymous user making the request is the legitimate owner of the cart associated with that token. This represents a fundamental authorization bypass where possession of the token alone grants full cart modification capabilities.
Attack Vector
The attack vector is network-based, allowing remote unauthenticated exploitation. An attacker needs to obtain a valid cart tokenValue belonging to another customer. This could be achieved through:
- Intercepting unencrypted traffic if HTTPS is not properly enforced
- Exploiting other information disclosure vulnerabilities
- Social engineering or phishing attacks that capture cart URLs
- Token enumeration if tokens are predictable
Once a valid token is obtained, the attacker sends a crafted POST request to the vulnerable endpoint with the target's tokenValue and arbitrary item data. The server processes this request without ownership verification, adding the attacker-specified items to the victim's cart. The full cart representation returned in the response (HTTP 201) provides the attacker with visibility into the victim's cart contents.
Detection Methods for CVE-2026-31821
Indicators of Compromise
- Unexpected items appearing in customer shopping carts
- Unusual patterns of cart modification requests from different IP addresses for the same cart token
- HTTP 201 responses on the /api/v2/shop/orders/{tokenValue}/items endpoint from unauthenticated sessions
- Customer complaints about cart tampering or unauthorized item additions
Detection Strategies
- Implement API request logging with correlation of cart tokens to authenticated sessions
- Monitor for cart modification patterns where the session owner differs from the cart owner
- Deploy Web Application Firewall (WAF) rules to detect anomalous cart API access patterns
- Review access logs for sequential or bulk requests to cart item endpoints across multiple token values
Monitoring Recommendations
- Enable detailed logging on all /api/v2/shop/orders/ endpoint access
- Configure alerts for cart modification attempts from IP addresses not associated with the cart's original session
- Monitor for sudden spikes in cart item addition requests that may indicate exploitation attempts
- Implement rate limiting on cart manipulation endpoints to slow enumeration attacks
How to Mitigate CVE-2026-31821
Immediate Actions Required
- Upgrade Sylius to version 2.0.16, 2.1.12, 2.2.3, or later immediately
- Review cart modification logs for signs of unauthorized access prior to patching
- Invalidate existing cart tokens and force regeneration for active sessions
- Consider implementing additional authentication requirements for cart modifications
Patch Information
Sylius has released security patches addressing this vulnerability in versions 2.0.16, 2.1.12, and 2.2.3. The fix implements proper cart ownership verification before allowing item additions. Organizations should upgrade to these patched versions immediately. For additional details, refer to the GitHub Security Advisory GHSA-wjmg-4cq5-m8hg.
Workarounds
- Implement a custom middleware or API gateway rule to validate cart ownership before requests reach the vulnerable endpoint
- Restrict access to the Shop API to authenticated users only until patching is complete
- Deploy WAF rules to block unauthenticated requests to the /api/v2/shop/orders/{tokenValue}/items endpoint
- Consider using session-bound cart identifiers instead of predictable or enumerable tokens as a defense-in-depth measure
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
