CVE-2021-42785 | Buffer Overflow in tvnviewer.exe via Crafted Packet in TightVNC Viewer 2.8.59

Buffer Overflow vulnerability in tvnviewer.exe of TightVNC Viewer allows a remote attacker to execute arbitrary instructions via a crafted FramebufferUpdate packet from a VNC server.

Published: 2021-11-23 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-42785 is rated High Risk (66.2/100): CVSS Critical severity, with medium exploitation likelihood (EPSS 0.98%). High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-42785

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-12 0.91% 0.98% +0.07%
2 2026-01-31 0.75% 0.91% +0.16%
3 2025-08-03 — 0.75% —

Full EPSS history (15 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-42785

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 5.9 [email protected]
7.5 2.0 HIGH
AV:N/AC:L/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 6.4 [email protected]

Weakness enumeration for CVE-2021-42785

OS Trackers for CVE-2021-42785

vendor priority summary link
suse high CVE-2021-42785 severity important: SUSE including 1 source package names (tightvnc), 3 product×package rows across 3 product lines (SUSE Linux Enterprise Server 11 SP1, SUSE Linux Enterprise Server 11 SP3, SUSE Linux Enterprise Server 11 SP4-LTSS): Known Not Affected 3. https://www.suse.com/security/cve/CVE-2021-42785/
ubuntu medium CVE-2021-42785 medium priority: Ubuntu including 1 source packages (tightvnc), 15 status rows across 15 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): not-affected 14, needed 1. https://ubuntu.com/security/CVE-2021-42785

Affected software / configurations for CVE-2021-42785

Vendor Product Version Raw CPE
tightvnc tightvnc <= 2.8.59 cpe:2.3:a:tightvnc:tightvnc:*:*:*:*:*:*:*:*

References for CVE-2021-42785

URL Tags
https://www.tightvnc.com/whatsnew.php Release Notes Vendor Advisory
cvelogic Threat Intelligence