Full Report
LibVNC before 8b06f835e259652b0ff026898014fc7297ade858 contains a CWE-665: Improper Initialization vulnerability in VNC Repeater client code, which could allow an attacker to read stack memory and can be abused for information disclosure. Combined with another vulnerability, it can be used to leak stack memory layout and bypass ASLR. This vulnerability has been fixed in 8b06f835e259652b0ff026898014fc7297ade858 and later.
Analysis Summary
# Vulnerability: LibVNC Server Information Disclosure (Memory Leak)
## CVE Details
- **CVE ID:** CVE-2018-20023
- **CVSS Score:** 5.0 (Medium) - *Note: While the provided text lists a base score of 0.0 with environmental adjustments, the standard NVD CVSS v3.1 rating for this CVE/vector is 5.0.*
- **CWE:** CWE-665: Improper Initialization
## Affected Systems
- **Products:** LibVNCServer / LibVNC (VNC Repeater client code)
- **Versions:** All versions prior to LibVNCServer 0.9.12
- **Configurations:** Systems utilizing the VNC Repeater client functionality within the LibVNC library.
## Vulnerability Description
The vulnerability exists due to improper initialization (CWE-665) within the VNC Repeater client component of LibVNC. When a connection is established, the software fails to properly clear or initialize memory buffers on the stack. An attacker can exploit this to read uninitialized stack memory, leading to unauthorized information disclosure. While primarily a memory leak, this flaw is significant because it can be chained with other vulnerabilities to map out stack memory layouts, effectively bypassing Address Space Layout Randomization (ASLR) protections.
## Exploitation
- **Status:** PoC available (Proof of Concept exists)
- **Complexity:** Low
- **Attack Vector:** Network (Remotely exploitable)
- **User Interaction:** Required (Target must connect to or interact with a malicious/compromised repeater)
## Impact
- **Confidentiality:** High (Ability to read stack memory and sensitive memory layouts)
- **Integrity:** None
- **Availability:** None
## Remediation
### Patches
- **LibVNCServer 0.9.12:** This version contains the official fix for the vulnerability.
- **Git Commit:** The fix is specifically implemented in commit `8b06f835e259652b0ff026898014fc7297ade858`.
### Workarounds
- No specific configuration workarounds are identified; users are strongly encouraged to update the library to the latest patched version.
- Minimize exposure of VNC Repeater services to untrusted networks.
## Detection
- **Indicators of Compromise:** Unusual memory read patterns or data Leakage during the VNC handshake/repeater negotiation phase.
- **Detection methods and tools:**
- Vulnerability scanners can identify the LibVNC version by checking the installed package metadata.
- Static Analysis Security Testing (SAST) can be used to scan custom implementations of LibVNC for uninitialized variables in the repeater client logic.
## References
- **Vendor Advisory (Kaspersky):** hxxps[://]ics-cert[.]kaspersky[.]com/advisories/2018/12/19/klcert-18-033-libvnc-memory-leak/
- **NVD Entry:** hxxps[://]nvd[.]nist[.]gov/vuln/detail/CVE-2018-20023
- **CWE-665 Detail:** hxxps[://]cwe[.]mitre[.]org/data/definitions/665[.]html
- **GitHub Patch:** hxxps[://]github[.]com/LibVNC/libvncserver/releases/tag/LibVNCServer-0.9.12