CVE-2023-27533
📋 TL;DR
A vulnerability in curl versions before 8.0 allows attackers to inject malicious content during TELNET protocol negotiation when user input is accepted. This could lead to arbitrary code execution on systems using vulnerable curl versions with TELNET functionality. Applications that process user input and use curl's TELNET capabilities are affected.
💻 Affected Systems
- curl
- libcurl
- applications using libcurl
📦 What is this software?
Curl by Haxx
curl is a command-line tool and library for transferring data with URLs. It supports numerous protocols including HTTP, HTTPS, FTP, and more, making it essential for API testing, web scraping, and automated data transfers.
Learn more about Curl →Fedora by Fedoraproject
⚠️ Risk & Real-World Impact
Worst Case
Remote code execution with the privileges of the curl-using application, potentially leading to full system compromise.
Likely Case
Unauthorized command execution, data exfiltration, or system manipulation through injected TELNET options.
If Mitigated
Limited impact if TELNET usage is restricted or input validation is implemented at application layer.
🎯 Exploit Status
Exploitation requires user input to be passed to curl's TELNET functionality. The vulnerability is well-documented with public proof-of-concept available.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: curl 8.0.0 and later
Vendor Advisory: https://curl.se/docs/CVE-2023-27533.html
Restart Required: Yes
Instructions:
1. Update curl to version 8.0.0 or later using your package manager. 2. For Linux: 'sudo apt update && sudo apt upgrade curl' (Debian/Ubuntu) or 'sudo yum update curl' (RHEL/CentOS). 3. Restart any services or applications using curl/libcurl.
🔧 Temporary Workarounds
Disable TELNET protocol support
linuxRecompile curl without TELNET protocol support if not needed
./configure --disable-telnet
make
sudo make install
Application-level input validation
allImplement strict input validation in applications using curl TELNET functionality
🧯 If You Can't Patch
- Disable TELNET protocol usage in all applications
- Implement network segmentation to isolate systems using curl TELNET functionality
🔍 How to Verify
Check if Vulnerable:
Check curl version with 'curl --version' and verify it's below 8.0.0Check Version:
curl --version | head -1Verify Fix Applied:
Confirm curl version is 8.0.0 or higher with 'curl --version'📡 Detection & Monitoring
Log Indicators:
- Unusual TELNET protocol usage in application logs
- Unexpected curl process execution with TELNET arguments
Network Indicators:
- TELNET traffic to unexpected destinations
- Malformed TELNET option negotiation packets
SIEM Query:
process.name:"curl" AND cmdline:"telnet://" AND NOT version:"8.0.*"🔗 References
- https://hackerone.com/reports/1891474
- https://lists.debian.org/debian-lts-announce/2023/04/msg00025.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/36NBD5YLJXXEDZLDGNFCERWRYJQ6LAQW/
- https://security.gentoo.org/glsa/202310-12
- https://security.netapp.com/advisory/ntap-20230420-0011/
- https://hackerone.com/reports/1891474
- https://lists.debian.org/debian-lts-announce/2023/04/msg00025.html
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/36NBD5YLJXXEDZLDGNFCERWRYJQ6LAQW/
- https://security.gentoo.org/glsa/202310-12
- https://security.netapp.com/advisory/ntap-20230420-0011/
