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TI-2026-06899 Aliases CVE-2026-7840GHSA-95qw-xpp9-h343

UltraVNC repeater HTTP server global buffer overflow via long URI (pre-auth RCE)

Priority MEDIUM 53CWE-787Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
None
Impact type
Code execution
Confidentiality · integrity · availability
High · High · High
Fix status
No fix listed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-787 and the CVSS impact.

Summary

UltraVNC repeater through 1.8.2.2 contains a global buffer overflow in its embedded HTTP administration server. The functions wi_senderr() and wi_replyhdr() in repeater/webgui/webutils.c write the caller-supplied HTTP request URI into a fixed 1000-byte global buffer (hdrbuf) via unchecked sprintf calls. The HTTP receive buffer accepts URIs up to approximately 150 KB (WI_RXBUFSIZE = 153600), so an unauthenticated attacker who can reach the repeater HTTP port (default TCP 80) can overflow hdrbuf by at least 500 bytes with a single HTTP request containing a URI of 1500 bytes or longer, corrupting adjacent .bss-segment globals. The overflow occurs before any authentication check, making it reachable without credentials. A remote, unauthenticated attacker can achieve arbitrary code execution on the host running the repeater.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.02628 85th percentileScored 2026-11-07
Fix No fix listed No fixed version in the sources yet

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
uvncUltraVNCup to 1.8.2.2—No fix listedCNA
  • UltraVNC Vendoruvnc Affected up to 1.8.2.2 Fixed in — No fix listed CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:uvnc:ultravnc:*:*:*:*:*:*:*:*up to 1.8.2.2Vulnerableuvnc
  • cpe:2.3:a:uvnc:ultravnc:*:*:*:*:*:*:*:* Versions up to 1.8.2.2 Vulnerable ·uvnc

Remediation

No fixed version listed by the sources yet.

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-7840
  2. 2026-10-03 Alias added: GHSA-95qw-xpp9-h343

References

Advisory 1

Other 2

  • TI-2020-19268 UltraVNC Launcher 1.2.4.0 - 'RepeaterHost' Denial of Service CVSS 4.0MEDIUM 6.7
  • TI-2026-04323 UltraVNC Service version.dll uncontrolled search path CVSS 4.0HIGH 7.3
  • TI-2020-19267 UltraVNC Launcher 1.2.4.0 - 'Password' Denial of Service CVSS 4.0MEDIUM 6.7
  • TI-2019-05946 Heap-based buffer overflow in Kaspersky Lab UltraVNC CVSS 3.1CRITICAL 9.8
  • TI-2019-05945 Heap-based buffer overflow in Kaspersky Lab UltraVNC CVSS 3.1CRITICAL 9.8
  • TI-2019-05943 Heap-based buffer overflow in Kaspersky Lab UltraVNC CVSS 3.1CRITICAL 9.8
See all 36 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences