Full Report
UltraVNC before 1.2.2.4 contains multiple memory leaks (CWE-665) in VNC server code, which allow an attacker to read stack memory and can be abused for information disclosure.
Analysis Summary
# Vulnerability: UltraVNC Improper Initialization Information Disclosure
## CVE Details
- **CVE ID:** CVE-2019-8277
- **CVSS Score:** 4.3 (Medium) - *Note: While the provided text lists a base score of 0.0, the vector string CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N calculates to 4.3.*
- **CWE:** CWE-665 (Improper Initialization)
## Affected Systems
- **Products:** UltraVNC (VNC Server component)
- **Versions:** All versions prior to 1.2.2.4
- **Configurations:** The vulnerability requires an attacker to have network access and for a user to be logged into the VNC server.
## Vulnerability Description
UltraVNC contains multiple instances of improper initialization (memory leaks) within the VNC server code. Specifically, the software fails to properly clear or initialize buffers before sending them across the network. This allows a remote authenticated attacker to read uninitialized data from the stack memory.
## Exploitation
- **Status:** PoC available
- **Complexity:** Low
- **Attack Vector:** Network (Remote)
- **Requirements:** Low Privileges (Authentication required)
## Impact
- **Confidentiality:** Low (Information Disclosure). An attacker can read stack memory, which can lead to the disclosure of sensitive internal pointers.
- **Integrity:** None
- **Availability:** None
- **Security Bypass:** This vulnerability can be specifically used to bypass **ASLR (Address Space Layout Randomization)**, facilitating more complex subsequent attacks (such as Remote Code Execution).
## Remediation
### Patches
- **Update to UltraVNC 1.2.2.4** or newer. This version contains the necessary fixes to properly initialize memory buffers.
### Workarounds
- Ensure the VNC server is not exposed to untrusted networks.
- Use strong authentication to prevent unauthorized users from gaining the "Low Privileges" status required to trigger the leak.
- Implement VPNs or SSH tunneling to restrict access to the VNC port (default 5900).
## Detection
- **Indicators of Compromise:** Unusual data patterns in VNC traffic that mirror stack structures or memory addresses.
- **Detection methods:** Monitor for unauthorized or anomalous connection attempts to VNC services. Use vulnerability scanners to identify outdated versions of UltraVNC (pre-1.2.2.4).
## References
- **Vendor Advisory:** [https://ics-cert.kaspersky[.]com/advisories/2019/03/01/klcert-19-024-ultravnc-improper-initialization/]
- **NVD Entry:** [https://nvd.nist[.]gov/vuln/detail/CVE-2019-8277]
- **CVSS Calculator:** [https://www.first[.]org/cvss/calculator/3.1#CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N/E:P/RL:O/RC:C]