Denial of Service in LLDAP via Malformed Refresh Token

Executive Summary

CVE-2026-50889 is a vulnerability in LLDAP version 0.6.2 related to how the application handles the HTTP refresh token header.

Specifically, when processing the refresh-token header in the /auth/refresh and /auth/logout endpoints, the function get_refresh_token() calls HeaderValue::to_str().unwrap(). This unwrap() call fails if the header contains non-ASCII bytes, causing the application to panic and crash the HTTP worker.

An attacker can exploit this by sending a crafted refresh-token header with non-ASCII data, such as byte 0xff, which triggers the crash.

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Impact Analysis

This vulnerability allows a remote unauthenticated attacker to cause a Denial of Service (DoS) by crashing the HTTP worker of the LLDAP server.

Under the default single-worker configuration, repeated exploitation can keep the server's HTTP interface unavailable or unstable, disrupting service availability.

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Detection Guidance

This vulnerability can be detected by monitoring for crashes or instability in the LLDAP v0.6.2 HTTP service, especially related to the /auth/refresh and /auth/logout endpoints.

To detect exploitation attempts, you can capture and analyze HTTP requests that contain a refresh-token header with non-ASCII or malformed bytes.

A practical approach is to use network traffic inspection tools like tcpdump or Wireshark to filter HTTP requests to these endpoints and check for suspicious refresh-token headers.

• Use tcpdump to capture HTTP traffic on port 80 or 443 (depending on your setup): tcpdump -i <interface> -A 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)'
• Filter captured traffic for requests to /auth/refresh or /auth/logout and inspect the refresh-token header for non-ASCII bytes (e.g., 0xff).
• Alternatively, use curl or similar tools to test the endpoints by sending crafted refresh-token headers with non-ASCII bytes and observe if the server crashes.

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Mitigation Strategies

Immediate mitigation steps include restricting or filtering incoming HTTP requests to the /auth/refresh and /auth/logout endpoints to block requests with malformed or non-ASCII refresh-token headers.

If possible, configure a web application firewall (WAF) or reverse proxy to validate and sanitize the refresh-token header before it reaches the LLDAP server.

Consider increasing the number of HTTP workers or enabling worker isolation to reduce the impact of a single worker crash.

Monitor server logs and uptime closely to detect and respond quickly to any denial-of-service conditions caused by this vulnerability.

Apply any available patches or updates from the LLDAP project that address this input handling flaw as soon as they are released.

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Compliance Impact

The provided information does not specify any direct impact of this vulnerability on compliance with common standards and regulations such as GDPR or HIPAA.

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