CVE-2026-50538

HIGHPre-NVD 8.88.8—
EchelonGraph scoreMEDIUM confidence

This high-severity CVE scores 8.8 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.3%, top 75% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
Trending — 3 sources updated this weekElevated
8.8EG
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 8.8Exploit: Elevated riskExposed: 0

A fix is available — apply it.

LibVNCClient is a library for easy implementation of a VNC client. In versions 0.9.12 through 0.9.15, a malicious (or man-in-the-middle) VNC server can force a connecting libvncclient to write attacker-controlled data past the end of its framebuffer. This is an out-of-bounds heap write with attacker-controlled length, contents, and offset. It needs no authentication (the attacker is the server), works in a default build with default settings, and fires from a single FramebufferUpdate the moment the victim connects. It crashes any client unconditionally (denial of service); we also demonstrated it overwriting an application callback pointer and redirecting execution to attacker-chosen code (code execution) under the default configuration. Commit 540332be3e0acc566fa64da6f1b4680c72c724dd patches the issue.

CVSS v3
8.8
EG Score
8.8(medium)
EG Risk
56(Track*)
EG Risk 56/100SSVC: 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
Severity88% × 45%
Exploitation40% × 40%
Automatability0% × 15%
Action: Watch closely — could escalate to Attend.
EPSS PROB
0%
EPSS %ILE
25%
KEV
Not listed

Published

August 21, 2026

Last Modified

August 24, 2026

Advisory Details (2)

Auto-updated Aug 21, 2026
🔬 Proof of concept available. Patch available. Sources: github_commit, github.
github Patch Available🟡 PoC Available

Attacker-controlled heap out-of-bounds write in libvncclient Tight decoder · Advisory · LibVNC/libvncserver · GitHub

https://github.com/LibVNC/libvncserver/security/advisories/GHSA-v9pm-47h4-jcq8
github_commit

commit 540332be3e0a (LibVNC/libvncserver)

Fix landed in LibVNC/libvncserver commit 540332be3e0a — awaiting tagged release

https://github.com/LibVNC/libvncserver/commit/540332be3e0acc566fa64da6f1b4680c72c724dd

Patch Availability(1)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntulibvncserver1 (0.9.15+dfsg-3ubuntu0.2) @ resolute2026-09-21ubuntu

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(3 across 3 ecosystems)
Debian:12(1)
PackageVulnerable rangeFixed inDependents
libvncserver0.9.14+dfsg-1, 0.9.14+dfsg-1+deb12u10.9.14+dfsg-1+deb12u2—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
libvncserver0.9.15+dfsg-1, 0.9.15+dfsg-1+deb13u10.9.15+dfsg-1+deb13u2—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
libvncserver0.9.15+dfsg-1, 0.9.15+dfsg-2, 0.9.15+dfsg-3, 0.9.15+dfsg-4, 0.9.15+dfsg-50.9.15+dfsg-6—

Weakness Classification(2)

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

All Vendor Advisories

(1)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 26× in last 7d / 101× 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 106 total refreshes for this CVE.

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

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2026-50538?
CVE-2026-50538 is a high vulnerability published on August 21, 2026. LibVNCClient is a library for easy implementation of a VNC client. In versions 0.9.12 through 0.9.15, a malicious (or man-in-the-middle) VNC server can force a connecting libvncclient to write attacker-controlled data past the end of its framebuffer. This is an out-of-bounds heap write with…
When was CVE-2026-50538 disclosed?
CVE-2026-50538 was first published in the National Vulnerability Database on August 21, 2026, with the most recent update on August 24, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-50538 actively exploited?
CVE-2026-50538 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 74.7% of all scored CVEs.
What is the CVSS score of CVE-2026-50538?
CVE-2026-50538 has a CVSS v3 base score of 8.8 (NVD).
How do I remediate CVE-2026-50538?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-50538, 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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