CVE-2024-0263: Acme Ultra Mini Httpd DoS Vulnerability

CVE-2024-0263 Overview

CVE-2024-0263 affects Acme Ultra Mini HTTPd version 1.21, a lightweight web server. The vulnerability resides in the HTTP GET request handler and allows remote attackers to trigger a denial-of-service (DoS) condition. The flaw is classified under [CWE-404] (Improper Resource Shutdown or Release). No authentication or user interaction is required to exploit the issue, and the attack can be launched over the network. Public exploit details have been disclosed, increasing the risk of opportunistic abuse against exposed instances. Administrators running Ultra Mini HTTPd 1.21 should treat any internet-facing deployment as exposed and apply the vendor patch promptly.

Critical Impact
Remote, unauthenticated attackers can crash the Ultra Mini HTTPd 1.21 service via crafted HTTP GET requests, disrupting availability of hosted content.

Affected Products

Acme Ultra Mini HTTPd 1.21
Deployments exposing the HTTP GET request handler to untrusted networks
Embedded or appliance environments bundling Ultra Mini HTTPd 1.21

Discovery Timeline

2024-01-07 - CVE-2024-0263 published to the National Vulnerability Database (NVD)
2024-11-21 - Last updated in the NVD database

Technical Details for CVE-2024-0263

Vulnerability Analysis

The vulnerability is a remote denial-of-service condition in the HTTP GET request handler of Acme Ultra Mini HTTPd 1.21. A remote attacker can manipulate request input processed by the GET handler to cause the server process to terminate or stop responding. The result is loss of availability for any content or services delivered by the affected instance. Because the server is commonly deployed as an embedded or lightweight HTTP front end, an outage can interrupt management consoles, file delivery, or device-status endpoints. The condition does not expose data confidentiality or integrity, but it does halt the request-serving pipeline until the daemon is restarted.

Root Cause

The issue maps to [CWE-404] Improper Resource Shutdown or Release. The GET handler fails to properly release or manage resources when processing certain request input, leaving the server in a state where it cannot continue handling client connections. Public references, including the Packet Storm Denial of Service advisory, document the crash behavior.

Attack Vector

Exploitation occurs over the network against the listening HTTP port. An attacker sends a crafted GET request to the vulnerable endpoint. No credentials, prior session, or user interaction are required. Additional technical context is published in the 0day Exploit Description and tracked as VulDB #249819. Because the exploit is publicly available, scanning and opportunistic abuse against exposed instances should be expected.

No verified proof-of-concept code is reproduced here. Refer to the linked advisories for technical request details.

Detection Methods for CVE-2024-0263

Indicators of Compromise

Unexpected termination or repeated restarts of the Ultra Mini HTTPd 1.21 process
Inbound HTTP GET requests with unusually long or malformed request lines targeting the server
Bursts of requests from a single source immediately preceding loss of service
Service-monitoring alerts reporting TCP port unresponsiveness on the HTTP listener

Detection Strategies

Enable verbose HTTP access and error logging on the Ultra Mini HTTPd host to capture the request that precedes a crash
Deploy a web application firewall (WAF) or reverse proxy to log and inspect inbound GET requests before they reach the server
Correlate process-exit events with network capture data to identify the triggering request
Compare current request patterns against a baseline of normal GET request size and structure

Monitoring Recommendations

Configure uptime monitoring for the HTTP listener and alert on consecutive failed health checks
Forward HTTP and process logs to a centralized SIEM for correlation across hosts
Track repeat source addresses sending malformed GET requests and feed them to perimeter blocklists

How to Mitigate CVE-2024-0263

Immediate Actions Required

Apply the vendor-supplied patch for Acme Ultra Mini HTTPd as soon as it is available
Restrict access to the HTTP service using firewall rules so only trusted networks can reach the listener
Place the server behind a reverse proxy or WAF capable of filtering malformed GET requests
Configure the host service manager to automatically restart the daemon if it terminates unexpectedly

Patch Information

The NVD entry recommends applying the vendor patch to remediate CVE-2024-0263. No vendor advisory URL is provided in the published references. Administrators should consult the VulDB #249819 entry and the VulDB CTI ID #249819 record for the latest remediation guidance, and verify the deployed Ultra Mini HTTPd build matches the patched release before returning the service to production.

Workarounds

Remove Ultra Mini HTTPd 1.21 from internet-facing exposure and bind the listener to internal interfaces only
Terminate inbound HTTP traffic at a hardened reverse proxy that enforces request-size and request-format limits
Rate-limit inbound GET requests per source address to reduce the impact of repeated crash attempts
If the server cannot be patched, evaluate migration to a maintained HTTP server for the affected workload

bash

# Example: restrict Ultra Mini HTTPd to a trusted management subnet using iptables
iptables -A INPUT -p tcp --dport 80 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP

# Example: systemd unit hardening to auto-restart the daemon on crash
# /etc/systemd/system/ultra-mini-httpd.service
# [Service]
# Restart=always
# RestartSec=5s
systemctl daemon-reload
systemctl restart ultra-mini-httpd