Home/CVE/Neat VNC is a VNC server library. Prior to 0.9.6, a pre-authentication stack buffer overflow exists in neatvnc in the RS
CVE
CVE-2026-42859
Neat VNC is a VNC server library. Prior to 0.9.6, a pre-authentication stack buffer overflow exists in neatvnc in the RS
Neat VNC is a VNC server library. Prior to 0.9.6, a pre-authentication stack buffer overflow exists in neatvnc in the RSA-AES security type handler. An unauthenticated remote attacker who can reach the VNC listening socket can send a crafted security type 5 (RSA-AES) or security type 129 (RSA-AES-256) handshake with an oversized client RSA public key, causing rsa_aes_send_challenge in src/auth/rsa-aes.c to overflow a 1024-byte on-stack buffer when encrypting the server challenge.
This results in at least a denial of service via server crash. This vulnerability is fixed in 0.9.6.
EPSS 0.00221
Schedule remediation
- SSVC automatable: yes - attacks can be scripted at scale
- ⚠ NVD has not scored this CVE yet - manual triage required (common for recent CVEs)
Sigma rules0
YARA rules0
Look this up elsewhere - one-click external pivots
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How to read a CVE - triage first, then detect and patch
This page is every public fact about CVE-2026-42859, 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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ATT&CK techniques
3Techniques this CVE enables - linked via CWECAPECATT&CK. High◆ = named directly in ATT&CK or Nuclei templates.
▤ Build a SIEM detection for these techniques▤
CAPEC attack patterns
12Attack patterns this CVE enables - the bridge from weakness to ATT&CK technique.
CAPEC-CAPEC-10 · Buffer Overflow via Environment Variables CAPEC-CAPEC-100 · Overflow Buffers CAPEC-CAPEC-14 · Client-side Injection-induced Buffer Overflow CAPEC-CAPEC-24 · Filter Failure through Buffer Overflow CAPEC-CAPEC-42 · MIME Conversion CAPEC-CAPEC-44 · Overflow Binary Resource File CAPEC-CAPEC-45 · Buffer Overflow via Symbolic Links CAPEC-CAPEC-46 · Overflow Variables and Tags CAPEC-CAPEC-47 · Buffer Overflow via Parameter Expansion CAPEC-CAPEC-67 · String Format Overflow in syslog() CAPEC-CAPEC-8 · Buffer Overflow in an API Call CAPEC-CAPEC-9 · Buffer Overflow in Local Command-Line Utilities
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Weakness Classification
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Scoring & Timeline
SSVC triage · cisa-vulnrichment
Exploitation
none
Automatable
yes
Technical impact
total
SSVC asks the questions that actually drive patch urgency: is it being exploited, can attacks be automated, and how total is the impact.
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References & Sources
2Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.