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 76% 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
24%
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) @ resolute2026-08-29ubuntu

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.

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 24× in last 7d / 34× 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. 2026-08-30 01:22 UTCEPSS rescore
  2. 2026-08-29 23:37 UTCVendor advisory
  3. 2026-08-29 12:34 UTCVendor advisory
  4. 2026-08-29 01:07 UTCEG score recompute
  5. 2026-08-28 21:41 UTCEPSS rescore
  6. 2026-08-28 02:58 UTCVendor advisory
  7. 2026-08-27 15:56 UTCEG score recompute
  8. 2026-08-27 14:25 UTCEPSS rescore
  9. 2026-08-27 04:54 UTCVendor advisory
  10. 2026-08-26 17:52 UTCEG score recompute
  11. 2026-08-26 17:52 UTCVendor advisory
  12. 2026-08-26 14:46 UTCEPSS rescore
  13. 2026-08-26 05:36 UTCVendor advisory
  14. 2026-08-25 18:33 UTCEG score recompute
  15. 2026-08-25 18:33 UTCVendor advisory
  16. 2026-08-25 13:49 UTCEPSS rescore
  17. 2026-08-25 07:31 UTCVendor advisory
  18. 2026-08-24 20:27 UTCEG score recompute
  19. 2026-08-24 20:27 UTCVendor advisory
  20. 2026-08-24 19:51 UTCEG score recompute
  21. 2026-08-24 19:51 UTCVendor advisory
  22. 2026-08-24 15:40 UTCEG score recompute
  23. 2026-08-24 15:40 UTCVendor advisory
  24. 2026-08-23 17:34 UTCVendor advisory
  25. 2026-08-23 06:31 UTCEG score recompute
Show 9 more
  1. 2026-08-23 06:31 UTCVendor advisory
  2. 2026-08-23 00:19 UTCEPSS rescore
  3. 2026-08-22 19:29 UTCVendor advisory
  4. 2026-08-22 08:26 UTCVendor advisory
  5. 2026-08-21 21:24 UTCEG score recompute
  6. 2026-08-21 21:24 UTCVendor advisory
  7. 2026-08-21 21:15 UTCEG score recompute
  8. 2026-08-21 21:15 UTCVendor advisory
  9. 2026-08-21 21:14 UTCMITRE cvelistV5first tracked

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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 75.6% 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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