CVE-2025-1451: Lollms Web UI DoS Vulnerability

CVE-2025-1451 Overview

CVE-2025-1451 affects parisneo/lollms-webui v13, an open-source web interface for large language model interactions. The vulnerability stems from improper handling of multipart boundaries during file uploads. The server fails to validate or constrain the length and content of boundary strings, enabling attackers to send requests with excessively long boundaries. This triggers resource exhaustion and leads to denial of service (DoS). A prior fix in commit 483431bb blocked hyphen characters appended to the boundary, but the patch is incomplete. Attackers can substitute alternative characters such as 4 or a to achieve the same impact, leaving the application exposed.

Critical Impact

Unauthenticated remote attackers can render the lollms-webui service unavailable by sending crafted multipart upload requests, disrupting access to hosted AI workloads.

Affected Products

• parisneo/lollms-webui v13
• cpe:2.3:a:lollms:lollms_web_ui:13:*:*:*:*:*:*:*
• Deployments running the unpatched multipart upload handler

Discovery Timeline

• 2025-03-20 - CVE-2025-1451 published to NVD
• 2025-10-15 - Last updated in NVD database

Technical Details for CVE-2025-1451

Vulnerability Analysis

The defect is categorized under [CWE-770] Allocation of Resources Without Limits or Throttling. The lollms-webui server parses multipart/form-data uploads without enforcing an upper bound on the boundary string. When a client submits a request with a boundary thousands or millions of characters long, the parser allocates memory and performs string operations proportional to that boundary across every part of the request. The cost scales linearly or worse, exhausting CPU and memory on the server.

The earlier remediation in commit 483431bb blocked hyphen (-) characters from being appended to the multipart boundary. This filter addresses only one character class. Attackers can replace hyphens with digits, alphabetic characters, or other tokens permitted by RFC 2046 boundary syntax. The parser continues to process these long boundaries, reproducing the exhaustion condition.

Root Cause

The handler accepts arbitrary boundary length and character composition. There is no maximum boundary size check, no global request size cap enforced before parsing, and no rate limiting on the upload endpoint. The hyphen-only filter from 483431bb is a character-level blocklist rather than a length constraint, leaving the underlying resource consumption pattern intact.

Attack Vector

The attack vector is network-based and requires no authentication or user interaction. An attacker sends an HTTP POST request to a file upload endpoint with a Content-Type: multipart/form-data; boundary=... header containing an oversized boundary built from non-hyphen characters. Repeated requests, or even a single sufficiently large request, consume server resources until the service becomes unresponsive. No code execution or data disclosure occurs, but availability is fully impacted.

Verified technical details are documented in the Huntr Vulnerability Report.

Detection Methods for CVE-2025-1451

Indicators of Compromise

• HTTP requests to lollms-webui upload endpoints with Content-Type: multipart/form-data headers containing boundary values longer than a few hundred bytes
• Boundary strings composed of repeated non-hyphen characters such as aaaa... or 4444...
• Sudden spikes in CPU or memory utilization on the lollms-webui process correlated with inbound multipart POST traffic
• Web server timeouts, 5xx responses, or process restarts immediately following large multipart uploads

Detection Strategies

• Inspect web access logs and reverse proxy logs for abnormally large Content-Type header values targeting lollms-webui routes
• Deploy WAF or reverse proxy rules that flag multipart boundaries exceeding 70 characters, the practical RFC 2046 limit
• Correlate process resource metrics with HTTP request patterns to identify exhaustion events triggered by single clients

Monitoring Recommendations

• Enable verbose logging on the lollms-webui upload routes and forward events to a centralized log platform
• Track per-source-IP request rates and request header sizes on upload endpoints
• Alert on repeated parser exceptions or worker process terminations within the application logs

How to Mitigate CVE-2025-1451

Immediate Actions Required

• Restrict access to lollms-webui upload endpoints to trusted networks until an updated release is available
• Deploy a reverse proxy or WAF in front of lollms-webui that enforces a hard limit on Content-Type header length and total request size
• Monitor the upstream parisneo/lollms-webui repository for a follow-up patch that supersedes commit 483431bb with length-based validation

Patch Information

At the time of NVD publication, no vendor advisory URL is listed beyond the Huntr Vulnerability Report. The prior fix in commit 483431bb is insufficient because it blocks only hyphen characters. Operators should track the project repository and apply any release that introduces explicit boundary length validation conforming to RFC 2046.

Workarounds

• Terminate TLS at a reverse proxy such as nginx and set client_max_body_size and large_client_header_buffers to conservative values
• Reject multipart requests with boundaries longer than 70 bytes at the proxy layer using header inspection rules
• Apply per-IP rate limiting on upload endpoints to slow exhaustion attempts
• Run lollms-webui under a process manager that enforces memory limits and automatic restarts to reduce downtime during attempted exploitation

# Example nginx configuration to reject oversized multipart boundaries
http {
    # Cap overall request size
    client_max_body_size 25m;
    # Limit header buffer allocation
    large_client_header_buffers 4 8k;

    map $http_content_type $bad_boundary {
        default 0;
        "~*boundary=[^;]{71,}" 1;
    }

    server {
        listen 443 ssl;
        location /upload {
            if ($bad_boundary) { return 400; }
            limit_req zone=uploads burst=5 nodelay;
            proxy_pass http://lollms_backend;
        }
    }
}