How severe is CVE-2026-7831?

CVE-2026-7831 has a CVSS 3.x base score of 7.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability high.

Is CVE-2026-7831 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (33rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-7831?

CVE-2026-7831 affects Uvnc Ultravnc. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-7831?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2026-7831 published?

CVE-2026-7831 was published on 2026-07-01 and last updated on 2026-07-02.

CVE-2026-7831

CVE-2026-7831 is a high-severity vulnerability in Uvnc Ultravnc with a CVSS 3.x base score of 7.6. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-193.

Key facts

Severity: High (CVSS 3.x base score 7.6)
EPSS exploit prediction: 0% (33rd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-193
Affected product: Uvnc Ultravnc
Published: 2026-07-01
Last modified: 2026-07-02

Description

UltraVNC viewer through 1.8.2.2 contains an off-by-one stack buffer overflow in the RFB ServerInit message handler. In vncviewer/ClientConnection.cpp, when the server-supplied nameLength equals exactly 2024 the code declares a 2024-byte stack buffer _dn[2024] and calls ReadString(_dn, 2024). ReadString writes the NUL terminator at buf[length], i.e., _dn[2024], one byte past the end of the stack buffer. A malicious VNC server can trigger this condition by advertising a desktop name of length 2024 in its ServerInit message. On release builds without stack canaries the single-byte NUL overwrite adjacent stack data. On builds with /GS stack protection the canary is corrupted and the process terminates, resulting in denial of service. User interaction (connecting the viewer to the malicious server) is required.

Frequently asked questions

What is CVE-2026-7831?: UltraVNC viewer through 1.8.2.2 contains an off-by-one stack buffer overflow in the RFB ServerInit message handler. In vncviewer/ClientConnection.cpp, when the server-supplied nameLength equals exactly 2024 the code declares a 2024-byte stack buffer _dn[2024] and calls ReadString(_dn, 2024). ReadString writes the NUL terminator at buf[length], i.e., _dn[2024], one byte past the end of the stack buffer. A malicious VNC server can trigger this condition by advertising a desktop name of length 2024 in its ServerInit message. On release builds without stack canaries the single-byte NUL overwrite adjacent stack data. On builds with /GS stack protection the canary is corrupted and the process terminates, resulting in denial of service. User interaction (connecting the viewer to the malicious server) is required.
How severe is CVE-2026-7831?: CVE-2026-7831 has a CVSS 3.x base score of 7.6, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity low, and availability high.
Is CVE-2026-7831 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (33rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-7831?: CVE-2026-7831 affects Uvnc Ultravnc. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-7831?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2026-7831 published?: CVE-2026-7831 was published on 2026-07-01 and last updated on 2026-07-02.

References

Affected products (1)

cpe:2.3:a:uvnc:ultravnc:*:*:*:*:*:*:*:*

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