Tightvnc: Improper Privilege Management
CVE-2023-27830 is a critical-severity improper privilege management vulnerability in Tightvnc, with a CVSS 3.1 base score of 9.0 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, but only if a user takes part, for example by opening a link or file. The record lists version 2.8.75 as the first without the flaw, so updating Tightvnc to that release or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 1.08% chance of exploitation within 30 days, higher than 66% of scored CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Tightvnc to 2.8.75 or a later version.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
Version data comes from NVD's product matching. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- RequiredA user must take an action such as opening a file or link.
- Scope
- ChangedThe attack can reach beyond the vulnerable component into other systems.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 9.0 | Critical | NVD |
| CVSS 3.1 | 9.0 | Critical | CISA (ADP) |
Official description
TightVNC before v2.8.75 allows attackers to escalate privileges on the host operating system via replacing legitimate files with crafted files when executing a file transfer. This is due to the fact that TightVNC runs in the backend as a high-privileges account.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Improper Privilege Management
The product does not properly assign, modify, track, or check privileges for an actor, creating an unintended sphere of control for that actor.
How developers prevent this class of flaw
- Very carefully manage the setting, management, and handling of privileges. Explicitly manage trust zones in the software.
- Follow the principle of least privilege when assigning access rights to entities in a software system.
- Consider following the principle of separation of privilege. Require multiple conditions to be met before permitting access to a system resource.
More Improper Privilege Management vulnerabilities (CWE-269)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- tightvnc.com/news.phpProduct, Release Notes
- tightvnc.com/whatsnew.phpProduct, Release Notes
Technical write-ups (may include proof of concept)
- medium.com/nestedif/vulnerability-disclosure-privilege-escalation-tightvnc-8165208cceExploit, Third Party Advisory
Recent Improper Privilege Management vulnerabilities
- 8.8 High severity
- 9.8 Critical severity
- 7.8 High severity
- 8.1 High severity
- 7.8 High severity
- 7.8 High severity
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