[NEW] [high] UltraVNC: Multiple vulnerabilities

CSIRTS triage

What

A remote, anonymous attacker can exploit multiple vulnerabilities in UltraVNC to execute arbitrary code, disclose confidential information, manipulate data, and cause a denial of service.

Who is affected

Deployments of UltraVNC.

Urgency

Remediation is high urgency due to the severity of the vulnerabilities and potential impacts.

Action

Apply patches or updates as soon as they are available.

AI-assisted analysis generated from the source advisory — verify against the original.

Details

Source

CERT-Bund (BSI) Security Advisories (DE · national-cert · site)

Severity

high

Published

2026-07-01

Exploitation

Not in CISA KEV at last sync

Language

Machine-translated to English — verify against the original

Original advisory: https://wid.cert-bund.de/portal/wid/securityadvisory?name=WID-SEC-2026-2162

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

• Low exploitation riskCVE-2026-440400.28% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 20% of all scored CVEs.
• Low exploitation riskCVE-2026-440410.32% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 23% of all scored CVEs.
• Low exploitation riskCVE-2026-440420.39% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 31% of all scored CVEs.
• Moderate exploitation riskCVE-2026-78281.1% 30-day exploitation probability. Patch within normal cadence, watch for KEV listing. Riskier than 60% of all scored CVEs.
• Low exploitation riskCVE-2026-78290.57% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 43% of all scored CVEs.
• Low exploitation riskCVE-2026-78300.22% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 12% of all scored CVEs.
• Low exploitation riskCVE-2026-78310.53% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 41% of all scored CVEs.
• Moderate exploitation riskCVE-2026-78381.4% 30-day exploitation probability. Patch within normal cadence, watch for KEV listing. Riskier than 69% of all scored CVEs.
• Low exploitation riskCVE-2026-78390.37% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 29% of all scored CVEs.
• Moderate exploitation riskCVE-2026-78401.4% 30-day exploitation probability. Patch within normal cadence, watch for KEV listing. Riskier than 70% of all scored CVEs.

Referenced CVEs

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

• criticalCVE-2026-7840: UltraVNC repeater through 1.8.2.2 contains a global buffer overflow in its embedded HTTP admini…nvd
• criticalCVE-2026-7839: UltraVNC repeater through 1.8.2.2 initializes the HTTP administration server with a hardcoded d…nvd
• highCVE-2026-7838: UltraVNC viewer through 1.8.2.2 contains an integer overflow leading to a heap buffer overflow …nvd
• highCVE-2026-7831: UltraVNC viewer through 1.8.2.2 contains an off-by-one stack buffer overflow in the RFB ServerI…nvd
• highCVE-2026-7830: UltraVNC through 1.8.2.2 uses inadequate cryptography in the MS-Logon II authentication scheme …nvd
• highCVE-2026-7829: UltraVNC repeater through 1.8.2.2 contains a post-authentication out-of-bounds write in the all…nvd
• mediumCVE-2026-7828: UltraVNC repeater through 1.8.2.2 contains an integer overflow in the HTTP request logging path…nvd
• lowCVE-2026-44042: UltraVNC repeater through 1.8.2.2 contains an off-by-one error in the Base64 decode helper use…nvd
• mediumCVE-2026-44041: UltraVNC through 1.8.2.2 contains an out-of-bounds read in the wide-string to multibyte conver…nvd
• mediumCVE-2026-44040: UltraVNC through 1.8.2.2 uses a cryptographically weak pseudo-random number generator to produ…nvd

Recent advisories for UltraVNC

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

• criticalCVE-2026-7840: UltraVNC repeater through 1.8.2.2 contains a global buffer overflow in its embedded HTTP admini…nvd · 2026-07-01
• criticalCVE-2026-7839: UltraVNC repeater through 1.8.2.2 initializes the HTTP administration server with a hardcoded d…nvd · 2026-07-01
• highCVE-2026-7838: UltraVNC viewer through 1.8.2.2 contains an integer overflow leading to a heap buffer overflow …nvd · 2026-07-01
• highCVE-2026-7831: UltraVNC viewer through 1.8.2.2 contains an off-by-one stack buffer overflow in the RFB ServerI…nvd · 2026-07-01
• highCVE-2026-7830: UltraVNC through 1.8.2.2 uses inadequate cryptography in the MS-Logon II authentication scheme …nvd · 2026-07-01
• highCVE-2026-7829: UltraVNC repeater through 1.8.2.2 contains a post-authentication out-of-bounds write in the all…nvd · 2026-07-01

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