Full Report
TigerVNC version prior to 1.10.1 is vulnerable to heap buffer overflow. Vulnerability could be triggered from CopyRectDecoder due to incorrect value checks. Exploitation of this vulnerability could potentially result into remote code execution. This attack appear to be exploitable via network connectivity.
Analysis Summary
# Vulnerability: Heap Buffer Overflow in TigerVNC leading to RCE
## CVE Details
- CVE ID: CVE-2019-15692
- CVSS Score: 9.8 (CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H/E:P/RL:O/RC:C derived score) - *Note: The provided CVSS vector simplifies to a Temporal Score indicating an existing exploit artifact, but the base impact is high.* **Interpreting the provided vector suggests a High severity result (assuming CVSS v3.x for the numeric calculation, which results in 8.8/9.8 depending on exact interpretation of the provided string's components vs standard interpretation of RCE impact).** We will stick to the High impact implied by RCE.
- CWE: (Not explicitly mentioned, but commonly tied to Buffer Errors)
## Affected Systems
- Products: TigerVNC
- Versions: Prior to 1.10.1
- Configurations: Standard network connectivity required for the connection.
## Vulnerability Description
TigerVNC versions before 1.10.1 are susceptible to a heap buffer overflow. This flaw is triggered within the `CopyRectDecoder` component due to insufficient or incorrect value checks, which can lead to memory corruption.
## Exploitation
- Status: PoC available (Implied by E:P in the CVSS vector suggesting an exploit artifact exists)
- Complexity: Low (AC:L - Attack Complexity Low)
- Attack Vector: Network (AV:N)
## Impact
- Confidentiality: High (C:H in vector)
- Integrity: High (I:H in vector)
- Availability: High (A:H in vector)
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*Note on User Interaction:* The provided CVSS vector includes `UI:R` (User Interaction Required). However, the text states "Exploitation of this vulnerability could potentially result into remote code execution," and the standard attack context suggests a direct remote connection is possible. Analysts should proceed assuming remote RCE is the primary risk, despite the UI requirement in the vector string.
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## Remediation
### Patches
- Update TigerVNC to version **1.10.1 or later** (Vendor released patch in December 2019).
### Workarounds
- No specific workarounds were detailed in the source text other than patching. Blocking or restricting access to VNC ports (typically 5900+) at the network perimeter should be considered if immediate patching is impossible.
## Detection
- Indicators of Compromise (IoCs) would involve monitoring VNC traffic for abnormal commands or data sizing directed toward the CopyRectDecoder logic, or monitoring associated processes for unexpected code execution or memory corruption events.
- Detection methods rely on strong network monitoring for the VNC protocol, specifically looking for malformed segments during image/rectangle transfer stages.
## References
- Vendor Advisory (Implicitly, the release of 1.10.1)
- Kaspersky Advisory: KLCERT-20-006 (Dated 23 March 2020)