CVE-2026-7840

CRITICALPre-NVD 9.89.8—
EchelonGraph scoreMEDIUM 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 — 3 sources updated this week
9.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 3%CVSS: 9.8Exploit: None knownExposed: 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(medium)
EG Risk
60(Track)
EG Risk 60/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity98% × 45%
Exploitation3% × 40%
Automatability100% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
3%
EPSS %ILE
85%
KEV
Not listed

Published

July 1, 2026

Last Modified

July 9, 2026

Advisory Details (3)

Auto-updated Sep 5, 2026
🔬 Proof of concept available. No patch confirmed yet.
generic🟡 PoC Available

CVE-2026-7840: Pre-auth Global Buffer Overflow in | Securin

https://www.securin.io/zero-days/cve-2026-7840-pre-auth-global-buffer-overflow-repeater-http-admin-ultravnc
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 8× in last 7d / 118× 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.

Showing the most recent 100 of 389 total refreshes for this CVE.

  1. 2026-09-11 14:53 UTCEPSS rescore
  2. 2026-09-11 14:53 UTCEPSS rescore
  3. 2026-09-08 22:01 UTCEPSS rescore
  4. 2026-09-06 14:28 UTCEG score recompute
  5. 2026-09-06 14:28 UTCGHSA enrichment
  6. 2026-09-06 13:48 UTCEPSS rescore
  7. 2026-09-06 02:57 UTCEG score recompute
  8. 2026-09-06 02:57 UTCGHSA enrichment
  9. 2026-09-04 05:07 UTCEPSS rescore
  10. 2026-09-02 14:12 UTCEPSS rescore
  11. 2026-09-01 13:54 UTCEPSS rescore
  12. 2026-09-01 04:40 UTCEPSS rescore
  13. 2026-09-01 04:40 UTCEPSS rescore
  14. 2026-08-31 01:10 UTCGHSA enrichment
  15. 2026-08-30 21:12 UTCEG score recompute
  16. 2026-08-30 21:12 UTCGHSA enrichment
  17. 2026-08-30 19:18 UTCEPSS rescore
  18. 2026-08-30 19:17 UTCEPSS rescore
  19. 2026-08-30 17:15 UTCGHSA enrichment
  20. 2026-08-30 13:18 UTCEG score recompute
  21. 2026-08-30 13:18 UTCGHSA enrichment
  22. 2026-08-30 01:22 UTCEPSS rescore
  23. 2026-08-28 21:42 UTCEPSS rescore
  24. 2026-08-28 02:48 UTCGHSA enrichment
  25. 2026-08-27 22:29 UTCEG score recompute
Show 75 more
  1. 2026-08-27 22:29 UTCGHSA enrichment
  2. 2026-08-27 14:25 UTCEPSS rescore
  3. 2026-08-26 14:47 UTCEPSS rescore
  4. 2026-08-25 13:49 UTCEPSS rescore
  5. 2026-08-25 04:59 UTCGHSA enrichment
  6. 2026-08-25 01:01 UTCGHSA enrichment
  7. 2026-08-24 21:03 UTCGHSA enrichment
  8. 2026-08-24 15:00 UTCEG score recompute
  9. 2026-08-24 15:00 UTCGHSA enrichment
  10. 2026-08-24 14:18 UTCEPSS rescore
  11. 2026-08-24 10:58 UTCEG score recompute
  12. 2026-08-24 10:58 UTCGHSA enrichment
  13. 2026-08-24 04:19 UTCGHSA enrichment
  14. 2026-08-24 00:21 UTCGHSA enrichment
  15. 2026-08-23 20:24 UTCGHSA enrichment
  16. 2026-08-23 16:27 UTCGHSA enrichment
  17. 2026-08-23 12:30 UTCGHSA enrichment
  18. 2026-08-23 08:33 UTCGHSA enrichment
  19. 2026-08-23 04:37 UTCGHSA enrichment
  20. 2026-08-23 00:40 UTCEG score recompute
  21. 2026-08-23 00:40 UTCGHSA enrichment
  22. 2026-08-23 00:19 UTCEPSS rescore
  23. 2026-08-22 20:08 UTCGHSA enrichment
  24. 2026-08-22 15:21 UTCGHSA enrichment
  25. 2026-08-22 11:24 UTCGHSA enrichment
  26. 2026-08-22 07:27 UTCGHSA enrichment
  27. 2026-08-22 01:13 UTCEG score recompute
  28. 2026-08-22 01:13 UTCGHSA enrichment
  29. 2026-08-21 23:49 UTCEPSS rescore
  30. 2026-08-21 21:15 UTCGHSA enrichment
  31. 2026-08-21 17:18 UTCGHSA enrichment
  32. 2026-08-21 12:42 UTCGHSA enrichment
  33. 2026-08-21 08:38 UTCGHSA enrichment
  34. 2026-08-21 04:41 UTCGHSA enrichment
  35. 2026-08-20 23:50 UTCEG score recompute
  36. 2026-08-20 23:50 UTCGHSA enrichment
  37. 2026-08-20 22:56 UTCEPSS rescore
  38. 2026-08-20 19:51 UTCGHSA enrichment
  39. 2026-08-20 15:54 UTCGHSA enrichment
  40. 2026-08-20 08:47 UTCGHSA enrichment
  41. 2026-08-20 04:50 UTCEG score recompute
  42. 2026-08-20 04:50 UTCGHSA enrichment
  43. 2026-08-19 17:04 UTCEPSS rescore
  44. 2026-08-19 14:16 UTCGHSA enrichment
  45. 2026-08-19 10:19 UTCGHSA enrichment
  46. 2026-08-19 05:34 UTCGHSA enrichment
  47. 2026-08-19 01:00 UTCGHSA enrichment
  48. 2026-08-18 21:02 UTCEG score recompute
  49. 2026-08-18 21:02 UTCGHSA enrichment
  50. 2026-08-18 13:49 UTCEPSS rescore
  51. 2026-08-18 13:49 UTCEPSS rescore
  52. 2026-08-18 04:53 UTCGHSA enrichment
  53. 2026-08-17 23:37 UTCGHSA enrichment
  54. 2026-08-17 14:02 UTCEG score recompute
  55. 2026-08-17 14:02 UTCGHSA enrichment
  56. 2026-08-17 13:47 UTCEPSS rescore
  57. 2026-08-17 10:05 UTCGHSA enrichment
  58. 2026-08-17 06:08 UTCGHSA enrichment
  59. 2026-08-17 02:02 UTCGHSA enrichment
  60. 2026-08-16 22:05 UTCGHSA enrichment
  61. 2026-08-16 18:08 UTCEG score recompute
  62. 2026-08-16 18:08 UTCGHSA enrichment
  63. 2026-08-16 14:56 UTCEPSS rescore
  64. 2026-08-16 14:56 UTCEPSS rescore
  65. 2026-08-16 13:30 UTCGHSA enrichment
  66. 2026-08-16 09:29 UTCGHSA enrichment
  67. 2026-08-16 05:32 UTCEG score recompute
  68. 2026-08-16 05:32 UTCGHSA enrichment
  69. 2026-08-16 02:15 UTCEPSS rescore
  70. 2026-08-16 01:35 UTCGHSA enrichment
  71. 2026-08-15 21:38 UTCGHSA enrichment
  72. 2026-08-15 17:40 UTCGHSA enrichment
  73. 2026-08-15 13:43 UTCGHSA enrichment
  74. 2026-08-15 09:39 UTCGHSA enrichment
  75. 2026-08-15 05:42 UTCGHSA enrichment

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, with the most recent update on July 9, 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 3% probability of exploitation in the next 30 days, which ranks it in the top 15.4% of all scored CVEs.
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

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