CVE-2025-1451: Lollms Web UI DoS Vulnerability

CVE-2025-1451 Overview

CVE-2025-1451 is a denial-of-service vulnerability in parisneo/lollms-webui v13, an open-source web interface for large language model interactions. The flaw resides in the server's handling of multipart boundaries during file upload processing. The server fails to validate or limit the length of the boundary string or the characters appended to it. Remote attackers can submit requests with excessively long boundaries to exhaust server resources and render the service unavailable. A prior fix in commit 483431bb blocked hyphen characters but did not address other characters such as 4 or a, leaving the underlying weakness exploitable [CWE-770].

Critical Impact
Unauthenticated remote attackers can trigger resource exhaustion and denial of service against any exposed lollms-webui v13 instance.

Affected Products

parisneo lollms-webui version 13
Deployments running the multipart upload handler
Instances that applied only the incomplete patch in commit 483431bb

Discovery Timeline

2025-03-20 - CVE-2025-1451 published to the National Vulnerability Database
2025-10-15 - Last updated in NVD database

Technical Details for CVE-2025-1451

Vulnerability Analysis

The vulnerability sits in the multipart/form-data parser used for file uploads. Multipart requests rely on a boundary string declared in the Content-Type header to separate parts. The lollms-webui server accepts boundaries of arbitrary length and does not constrain the characters that may be appended to them. When the server receives crafted requests with extremely long boundaries, parsing consumes excessive CPU and memory until the service becomes unresponsive.

The maintainers attempted a fix in commit 483431bb by rejecting boundary strings that contained appended hyphen characters. The patch addressed only a single character class. Attackers can substitute alphanumeric characters such as 4 or a and bypass the filter while reproducing the same resource exhaustion behavior. This classifies as Allocation of Resources Without Limits or Throttling [CWE-770].

Root Cause

The root cause is missing input validation on the multipart boundary token. The server treats the boundary as untrusted but unbounded user data. There is no maximum length check, no character allowlist, and no parsing timeout. The incomplete patch addressed symptoms rather than the underlying lack of boundary length enforcement.

Attack Vector

An unauthenticated remote attacker sends HTTP POST requests to any file upload endpoint with a Content-Type: multipart/form-data; boundary=<excessively long string> header. The boundary string contains characters not blocked by the existing patch. Repeated requests amplify resource consumption and cause sustained denial of service. The vulnerability requires no authentication, no user interaction, and only network access to the exposed service.

Detection Methods for CVE-2025-1451

Indicators of Compromise

HTTP requests with abnormally long boundary= values in the Content-Type header, typically exceeding several kilobytes
Multipart boundary strings containing repeated non-hyphen filler characters such as aaaa... or 4444...
Sudden spikes in CPU and memory utilization on lollms-webui processes during upload handling
Increasing request latency or 5xx responses from upload endpoints under low external traffic

Detection Strategies

Inspect HTTP traffic at the proxy or WAF layer for Content-Type headers where the boundary parameter exceeds a reasonable threshold (for example, 200 bytes)
Correlate process resource exhaustion events on hosts running lollms-webui with inbound multipart upload requests
Alert on repeated POST requests from a single source IP targeting upload routes within short time windows

Monitoring Recommendations

Enable verbose access logging on the lollms-webui reverse proxy and retain full Content-Type header values
Track per-process CPU and memory baselines for the lollms-webui service and alert on sustained deviations
Monitor application availability with synthetic checks against upload endpoints to detect early degradation

How to Mitigate CVE-2025-1451

Immediate Actions Required

Restrict network exposure of lollms-webui to trusted networks or place it behind an authenticated reverse proxy
Enforce a maximum Content-Type header length and a maximum multipart boundary length at the proxy or WAF layer
Apply request rate limits to upload endpoints to reduce the impact of repeated abusive requests
Review server logs for prior exploitation attempts using oversized boundaries

Patch Information

No complete fix is referenced in the published advisory. The earlier commit 483431bb is insufficient because it blocks only hyphen characters appended to the boundary. Operators should monitor the Huntr Bug Bounty Listing and the upstream parisneo/lollms-webui repository for an updated patch that enforces a strict boundary length limit and character allowlist.

Workarounds

Deploy a WAF rule that rejects multipart requests where the boundary parameter exceeds 70 bytes, which aligns with the RFC 2046 maximum
Terminate TLS at a reverse proxy that normalizes and validates Content-Type headers before forwarding to lollms-webui
Disable or block file upload routes if upload functionality is not required in the deployment

bash

# Example NGINX configuration to bound Content-Type header size and limit upload rate
http {
    large_client_header_buffers 4 1k;
    client_max_body_size 10m;

    limit_req_zone $binary_remote_addr zone=uploads:10m rate=5r/s;

    server {
        location /upload {
            limit_req zone=uploads burst=10 nodelay;
            if ($http_content_type ~* "boundary=[^;]{200,}") {
                return 400;
            }
            proxy_pass http://lollms_backend;
        }
    }
}