CVE-2026-7840

CRITICALPre-NVD 9.89.8—
EchelonGraph scoreHIGH confidence

Score 9.8 from GitHub Security Advisory (severity: CRITICAL) published 2026-07-01. a secondary CVSS source baseline 9.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, secondary
Trending — 4 sources updated this week
9.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 1%CVSS: 9.8Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
9.8
EG Score
9.8(high)
EPSS
64.5%
KEV
Not listed

Published

July 1, 2026

Last Modified

July 1, 2026

Advisory Details (2)

Auto-updated Jul 3, 2026
No patch confirmed yet.
generic

Home - UltraVNC VNC OFFICIAL SITE, Remote Desktop Free Opensource

https://uvnc.com/
generic

GitHub - ultravnc/UltraVNC: 👁️ UltraVNC Server, UltraVNC Viewer, UltraVNC Repeater and UltraVNC SC | Official repository: https://github.com/ultravnc/UltraVNC · GitHub

https://github.com/ultravnc/UltraVNC

Vendor Advisories for CVE-2026-7840(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 83× in last 7d / 83× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-07 04:20 UTCEG score recompute
  2. 2026-07-07 04:20 UTCGHSA enrichment
  3. 2026-07-07 00:23 UTCEG score recompute
  4. 2026-07-07 00:22 UTCGHSA enrichment
  5. 2026-07-06 20:25 UTCEG score recompute
  6. 2026-07-06 20:24 UTCGHSA enrichment
  7. 2026-07-06 16:27 UTCEG score recompute
  8. 2026-07-06 16:27 UTCGHSA enrichment
  9. 2026-07-06 16:27 UTCEPSS rescore
  10. 2026-07-06 16:27 UTCEPSS rescore
  11. 2026-07-06 12:23 UTCEG score recompute
  12. 2026-07-06 12:23 UTCGHSA enrichment
  13. 2026-07-06 08:24 UTCEG score recompute
  14. 2026-07-06 08:24 UTCGHSA enrichment
  15. 2026-07-06 04:26 UTCEG score recompute
  16. 2026-07-06 04:25 UTCGHSA enrichment
  17. 2026-07-06 02:23 UTCEPSS rescore
  18. 2026-07-06 02:23 UTCEPSS rescore
  19. 2026-07-06 00:24 UTCEG score recompute
  20. 2026-07-06 00:24 UTCGHSA enrichment
  21. 2026-07-05 20:27 UTCEG score recompute
  22. 2026-07-05 20:27 UTCGHSA enrichment
  23. 2026-07-05 16:29 UTCEG score recompute
  24. 2026-07-05 16:29 UTCGHSA enrichment
  25. 2026-07-05 12:28 UTCEG score recompute
Show 58 more
  1. 2026-07-05 12:28 UTCGHSA enrichment
  2. 2026-07-05 08:29 UTCEG score recompute
  3. 2026-07-05 08:29 UTCGHSA enrichment
  4. 2026-07-05 04:32 UTCEG score recompute
  5. 2026-07-05 04:32 UTCGHSA enrichment
  6. 2026-07-05 02:31 UTCEPSS rescore
  7. 2026-07-05 02:30 UTCEPSS rescore
  8. 2026-07-05 00:34 UTCEG score recompute
  9. 2026-07-05 00:34 UTCGHSA enrichment
  10. 2026-07-04 20:36 UTCEG score recompute
  11. 2026-07-04 20:36 UTCGHSA enrichment
  12. 2026-07-04 16:39 UTCEG score recompute
  13. 2026-07-04 16:39 UTCGHSA enrichment
  14. 2026-07-04 12:31 UTCEG score recompute
  15. 2026-07-04 12:31 UTCGHSA enrichment
  16. 2026-07-04 08:35 UTCEG score recompute
  17. 2026-07-04 08:35 UTCGHSA enrichment
  18. 2026-07-04 06:31 UTCEPSS rescore
  19. 2026-07-04 06:31 UTCEPSS rescore
  20. 2026-07-04 04:38 UTCEG score recompute
  21. 2026-07-04 04:38 UTCGHSA enrichment
  22. 2026-07-04 00:40 UTCEG score recompute
  23. 2026-07-04 00:40 UTCGHSA enrichment
  24. 2026-07-03 20:43 UTCEG score recompute
  25. 2026-07-03 20:43 UTCGHSA enrichment
  26. 2026-07-03 16:46 UTCEG score recompute
  27. 2026-07-03 16:45 UTCGHSA enrichment
  28. 2026-07-03 12:47 UTCEG score recompute
  29. 2026-07-03 12:47 UTCGHSA enrichment
  30. 2026-07-03 08:49 UTCEG score recompute
  31. 2026-07-03 08:49 UTCGHSA enrichment
  32. 2026-07-03 04:52 UTCEG score recompute
  33. 2026-07-03 04:52 UTCGHSA enrichment
  34. 2026-07-03 00:53 UTCEG score recompute
  35. 2026-07-03 00:52 UTCGHSA enrichment
  36. 2026-07-02 20:55 UTCEG score recompute
  37. 2026-07-02 20:55 UTCGHSA enrichment
  38. 2026-07-02 16:59 UTCEG score recompute
  39. 2026-07-02 16:59 UTCGHSA enrichment
  40. 2026-07-02 13:02 UTCEG score recompute
  41. 2026-07-02 13:02 UTCGHSA enrichment
  42. 2026-07-02 09:03 UTCEG score recompute
  43. 2026-07-02 09:03 UTCGHSA enrichment
  44. 2026-07-02 05:04 UTCEG score recompute
  45. 2026-07-02 05:04 UTCGHSA enrichment
  46. 2026-07-02 01:07 UTCEG score recompute
  47. 2026-07-02 01:07 UTCGHSA enrichment
  48. 2026-07-01 21:10 UTCEG score recompute
  49. 2026-07-01 21:10 UTCGHSA enrichment
  50. 2026-07-01 17:13 UTCEG score recompute
  51. 2026-07-01 17:13 UTCGHSA enrichment
  52. 2026-07-01 15:07 UTCEPSS rescore
  53. 2026-07-01 13:16 UTCEG score recompute
  54. 2026-07-01 13:16 UTCGHSA enrichment
  55. 2026-07-01 09:18 UTCEG score recompute
  56. 2026-07-01 09:18 UTCGHSA enrichment
  57. 2026-07-01 05:21 UTCEG score recompute
  58. 2026-07-01 05:20 UTCNVD updatefirst tracked

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-7840?
CVE-2026-7840 is a critical vulnerability published on July 1, 2026. UltraVNC repeater through 1.8.2.2 contains a global buffer overflow in its embedded HTTP administration server. The functions wisenderr() and wireplyhdr() in repeater/webgui/webutils.c write the caller-supplied HTTP request URI into a fixed 1000-byte global buffer (hdrbuf) via unchecked sprintf…
When was CVE-2026-7840 disclosed?
CVE-2026-7840 was first published in the National Vulnerability Database on July 1, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-7840 actively exploited?
CVE-2026-7840 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 64.5% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-7840?
CVE-2026-7840 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2026-7840?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-7840, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

Explore the affected products and dependency analysis for CVE-2026-7840

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