CVE-2025-26699: Django wrap() Method DoS Vulnerability

CVE-2025-26699 Overview

A denial-of-service vulnerability has been identified in Django's text handling utilities. The django.utils.text.wrap() method and the wordwrap template filter are vulnerable to resource exhaustion attacks when processing very long strings. This vulnerability allows unauthenticated remote attackers to cause service disruption by submitting crafted payloads that trigger excessive CPU consumption during text wrapping operations.

Critical Impact

Remote attackers can exploit this vulnerability to cause denial of service conditions in Django applications that process user-controlled text through the wrap() method or wordwrap template filter, potentially making web applications unresponsive.

Affected Products

• Django 5.1 before 5.1.7
• Django 5.0 before 5.0.13
• Django 4.2 before 4.2.20
• Debian Linux 11.0

Discovery Timeline

• 2025-03-06 - Security patches released by Django
• 2025-03-06 - CVE-2025-26699 published to NVD
• 2025-10-03 - Last updated in NVD database

Technical Details for CVE-2025-26699

Vulnerability Analysis

This vulnerability is classified as CWE-770 (Allocation of Resources Without Limits or Throttling). The django.utils.text.wrap() method and its corresponding wordwrap template filter are designed to wrap text at a specified line width. However, the implementation lacks proper resource management when handling exceptionally long input strings.

When a malicious user supplies a very long string without natural word boundaries (such as spaces or hyphens), the text wrapping algorithm enters a computationally expensive operation attempting to find appropriate break points. This algorithmic complexity issue results in excessive CPU consumption that can be exploited to deny service to legitimate users.

The network-accessible nature of this vulnerability means that any Django application exposing functionality that processes user input through these text utilities is potentially at risk. No authentication or special privileges are required to exploit this flaw.

Root Cause

The root cause lies in the insufficient input validation and resource management within the text wrapping implementation. The wrap() method does not impose limits on the computational resources allocated when processing input strings, allowing attackers to trigger resource exhaustion scenarios by submitting specially crafted long strings that maximize processing overhead.

Attack Vector

The vulnerability is exploitable over the network without requiring authentication. An attacker can craft HTTP requests containing very long strings that will be processed by Django's wrap() method or wordwrap template filter. When these long strings lack natural word boundaries, the text wrapping algorithm must perform extensive processing to determine appropriate line breaks, consuming significant CPU resources.

The attack is particularly effective because:

• No authentication is required to trigger the vulnerability
• The attack can be launched from any network-connected location
• A single malicious request with a sufficiently long string can consume substantial server resources

Detection Methods for CVE-2025-26699

Indicators of Compromise

• Abnormal CPU spikes on Django application servers coinciding with HTTP requests containing unusually long strings
• HTTP request logs showing requests with extremely large body sizes or query parameters
• Application response time degradation or timeouts during periods of suspicious traffic
• Memory consumption anomalies in Django worker processes

Detection Strategies

• Implement request monitoring to identify HTTP requests with payload sizes exceeding normal operational thresholds
• Configure application performance monitoring (APM) tools to alert on unusual CPU consumption patterns
• Analyze web server access logs for requests with abnormally large content-length headers
• Deploy web application firewall (WAF) rules to detect and block requests containing very long unbroken text strings

Monitoring Recommendations

• Configure alerts for sustained elevated CPU usage on Django application servers
• Monitor request duration metrics to identify potential DoS conditions
• Implement rate limiting and request size limits at the reverse proxy or load balancer level
• Review Django application logs for errors related to text processing timeouts

How to Mitigate CVE-2025-26699

Immediate Actions Required

• Upgrade Django 5.1 installations to version 5.1.7 or later
• Upgrade Django 5.0 installations to version 5.0.13 or later
• Upgrade Django 4.2 installations to version 4.2.20 or later
• Review application code for uses of django.utils.text.wrap() and the wordwrap template filter with user-controlled input

Patch Information

Django has released security patches addressing this vulnerability. The fix is included in the following versions:

• Django 5.1.7
• Django 5.0.13
• Django 4.2.20

For detailed patch information, refer to the Django Security Release Notes and the Django Security Releases Weblog. Debian users should apply updates from the Debian LTS Announcement.

Workarounds

• Implement input validation to limit the maximum length of strings processed by wrap() or wordwrap
• Configure web server or reverse proxy request size limits to reject abnormally large payloads
• Add rate limiting to endpoints that process user-provided text content
• Consider implementing request timeouts at the application level for text processing operations

# Configuration example - nginx request size limit
# Add to nginx server or location block
client_max_body_size 1m;
client_body_buffer_size 16k;

# Rate limiting configuration
limit_req_zone $binary_remote_addr zone=textproc:10m rate=10r/s;
limit_req zone=textproc burst=20 nodelay;