CVE-2023-38039
📋 TL;DR
CVE-2023-38039 is a memory exhaustion vulnerability in curl/libcurl where a malicious server can send unlimited HTTP headers, causing curl to consume all available heap memory and crash. This affects all applications using vulnerable curl versions to retrieve HTTP responses. Both client applications and systems making HTTP requests are vulnerable.
💻 Affected Systems
- curl
- libcurl
- any software 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
Fedora by Fedoraproject
Fedora by Fedoraproject
Windows 10 1809 by Microsoft
Windows 10 21h2 by Microsoft
Windows 10 22h2 by Microsoft
Windows 11 21h2 by Microsoft
Windows 11 22h2 by Microsoft
Windows 11 23h2 by Microsoft
⚠️ Risk & Real-World Impact
Worst Case
Complete denial of service through memory exhaustion, potentially crashing the application or system using curl, leading to service disruption.
Likely Case
Application crashes or becomes unresponsive when connecting to malicious servers, causing service interruptions.
If Mitigated
Minimal impact with proper input validation, rate limiting, and network segmentation in place.
🎯 Exploit Status
Exploitation requires curl to connect to a malicious server, which can be achieved through phishing, compromised websites, or man-in-the-middle attacks.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: curl 8.4.0 and later
Vendor Advisory: https://curl.se/docs/CVE-2023-38039.html
Restart Required: Yes
Instructions:
1. Update curl to version 8.4.0 or later. 2. For Linux: Use package manager (apt-get update && apt-get upgrade curl, yum update curl, etc.). 3. For Windows: Download latest from curl.se. 4. Rebuild applications using libcurl with updated library. 5. Restart affected services.
🔧 Temporary Workarounds
Limit HTTP header size via curl options
allSet maximum header size using CURLOPT_MAXFILESIZE_LARGE or similar options in application code
curl_easy_setopt(curl, CURLOPT_MAXFILESIZE_LARGE, (curl_off_t)1048576); // 1MB limit
Network filtering
allUse WAF or proxy to filter/limit HTTP header sizes before reaching curl
🧯 If You Can't Patch
- Implement network segmentation to restrict curl connections to trusted servers only
- Monitor memory usage of curl processes and implement automatic restart thresholds
🔍 How to Verify
Check if Vulnerable:
Run 'curl --version' and check if version is between 7.9.1 and 8.3.0 inclusiveCheck Version:
curl --version | head -1Verify Fix Applied:
Verify curl version is 8.4.0 or later with 'curl --version'📡 Detection & Monitoring
Log Indicators:
- Unusual memory consumption by curl processes
- curl process crashes or restarts
- High number of HTTP requests with large headers
Network Indicators:
- HTTP responses with abnormally large headers
- Connections to suspicious servers from curl processes
SIEM Query:
process_name="curl" AND (memory_usage>threshold OR exit_code!=0)🔗 References
- http://seclists.org/fulldisclosure/2023/Oct/17
- http://seclists.org/fulldisclosure/2024/Jan/34
- http://seclists.org/fulldisclosure/2024/Jan/37
- http://seclists.org/fulldisclosure/2024/Jan/38
- https://hackerone.com/reports/2072338
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/5DCZMYODALBLVOXVJEN2LF2MLANEYL4F/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/M6KGKB2JNZVT276JYSKI6FV2VFJUGDOJ/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TEAWTYHC3RT6ZRS5OZRHLAIENVN6CCIS/
- https://security.gentoo.org/glsa/202310-12
- https://security.netapp.com/advisory/ntap-20231013-0005/
- https://support.apple.com/kb/HT214036
- https://support.apple.com/kb/HT214057
- https://support.apple.com/kb/HT214058
- https://support.apple.com/kb/HT214063
- https://www.insyde.com/security-pledge/SA-2023064
- http://seclists.org/fulldisclosure/2023/Oct/17
- http://seclists.org/fulldisclosure/2024/Jan/34
- http://seclists.org/fulldisclosure/2024/Jan/37
- http://seclists.org/fulldisclosure/2024/Jan/38
- https://hackerone.com/reports/2072338
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/5DCZMYODALBLVOXVJEN2LF2MLANEYL4F/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/M6KGKB2JNZVT276JYSKI6FV2VFJUGDOJ/
- https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TEAWTYHC3RT6ZRS5OZRHLAIENVN6CCIS/
- https://security.gentoo.org/glsa/202310-12
- https://security.netapp.com/advisory/ntap-20231013-0005/
- https://support.apple.com/kb/HT214036
- https://support.apple.com/kb/HT214057
- https://support.apple.com/kb/HT214058
- https://support.apple.com/kb/HT214063
- https://www.insyde.com/security-pledge/SA-2023064
