CVE-2026-7831

Home/CVE/UltraVNC viewer through 1.8.2.2 contains an off-by-one stack buffer overflow in the RFB ServerInit message handler. In v

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UltraVNC viewer through 1.8.2.2 contains an off-by-one stack buffer overflow in the RFB ServerInit message handler. In v

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.

HIGH · CVSS 7.6 EPSS 0.00416

EPSS exploitation odds0.42% · top 66%

Schedule remediation

CVSS base score ≥ 7.0

No Sigma yet — build one → YARA rules0

Look this up elsewhere - one-click external pivots

NVD CVE.org CISA Exploit-DB GitHub PoC VulnCheck KEV GreyNoise

▸ How to read a CVE - triage first, then detect and patch

This page is every public fact about CVE-2026-7831, cross-linked. Its job is to answer one question fast - does this need my attention now? - and then hand you the two things you do about it. Here is how an analyst reads it.

Triage: should I act now? Four signals, and they are not interchangeable:

CVSSseverity - how bad it is IF exploited, 0-10. A high CVSS alone is not urgency; a flaw can be a perfect 10 and never actually be attacked. EPSSprobability - a model’s estimate of the chance it is exploited in the next 30 days, 0-1. This is the “will it actually happen” signal. CISA KEVconfirmed - it is being exploited in the wild right now. The strongest signal on the page; KEV beats any score. Weaponisedavailability - public exploits / PoCs, and especially Metasploit modules rated Excellent / Great. Reliable, packaged exploit code means low-skill attackers can use it today.

How they combine: KEV, or a dependable Metasploit module, means patch now regardless of CVSS. High CVSS + low EPSS + no exploit is real but not an emergency - schedule it. Low CVSS but KEV-listed still gets patched now. The verdict above already weighed these for you; this is how it got there.

Then what - two workflows:

Detectwhen you cannot patch today, follow this CVE to the ATT&CK techniques it enables, then Build a SIEM detection (the green button) - author a rule, test it in Atomic, deploy it. That buys visibility while the patch waits. PatchAffected products / packages tell you if you are exposed; Fixed versions by distribution and Vendor advisories give the exact version that closes it.

Reading order for the panels below: verdict + badges, then Public exploits / Metasploit (is it weaponised), then ATT&CK techniques + Sigma / IDS rules (can I detect it), then Affected products / packages + Fixed versions (am I exposed, what patches it), then Threat actors / IOCs (who uses it), then Scoring & timeline / references (the evidence).

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Severity & exploitation scoring

View on NVD →

CVSS base score

7.6

HIGHCVSS v3.1 · 33c584b5-0579-4c06-b2a0-8d8329fcab9c

EPSS exploitation probability

0.42%

Top 66%odds of exploitation in the next 30 days

CVSS metric silhouette

shape grows toward worst-case

SSVC triage · cisa-vulnrichment

Exploitation

none

Automatable

Tech impact

partial

CVSS vector breakdown

Exploitability - how they get in

Attack Vector

Network Adjacent Local Physical

Attack Complexity

Low High

Privileges Required

None Low High

User Interaction

None Required

Scope

Unchanged Changed

Impact - what breaks

Confidentiality

None Low High

Integrity

None Low High

Availability

None Low High

VECTORCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H

Attack path

Full kill chain

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ATT&CK techniques

Techniques this CVE enables. Pills with a solid outline are high confidence - named directly in ATT&CK or Nuclei, or human-curated by CTID; the rest are inferred from the weakness type using MITRE's CVE Mapping Methodology and the CWE → CAPEC chain. Broad, generic-weakness guesses are filtered out. A small N× marks a technique that N independent sources agree on.

T1499 · Endpoint Denial of Service

▤ Build a SIEM detection for these techniques