CVE-2026-50538

HIGHPre-NVD 8.88.8
EchelonGraph scoreMEDIUM confidence

“—” beside the score: it is equal to the CVSS score beside it.

This high-severity CVE scores 8.8 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.4% (32nd percentile of EPSS-scored CVEs). No GitHub Security Advisory CVSS is on record for this CVE.

Triggered by: Headline CVSS from a secondary CVSS source
Sources: EPSS, a secondary CVSS source
Trending — 3 sources updated this weekElevated
8.8EG
EchelonGraph verdictPlan a fixRemediate within your standard update timelines at low or medium mission impact and sooner than that at high (the SSVC decision on this page).
  • CISA's Vulnrichment rates exploitation as PoC; EchelonGraph holds no exploit-code reference for it
CISA-KEV: Not listedEPSS PROB: 0.4%CVSS: 8.8Exploit: No code on recordExposed services: Not assessed

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
8.8HIGHmedium confidence
EG Risk
56
EG Risk 56/100

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 (value × EchelonGraph’s weight)
Severity88% × 45%
The EG Score, 8.8 of 10.
Exploitation40% × 40%
EchelonGraph's fixed weight for EG-KEV Tier 3 (Elevated): a constant, not a probability.
Automatability0% × 15%
CISA's SSVC Automatable value: no (Vulnrichment).
SSVC (CISA's decision table, applied by EchelonGraph): Track at low, Track* at medium and Attend at high mission impact.
Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.
Action: A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.
EPSS PROB
0.4%
EPSS %ILE
32nd
KEV
Not listed

SSVC (CISA's decision table, applied by EchelonGraph)Track at low, Track* at medium and Attend at high mission impact.

A fix is available. Apply it within your standard update timelines at low or medium mission impact and sooner than that at high.

Exploitation public PoC (CISA Vulnrichment) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). All three are CISA's SSVC values (Vulnrichment). EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table

BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.

In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA Vulnrichment) · Technical impact total (CISA Vulnrichment). Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it

Published

August 21, 2026

Last Modified

October 12, 2026

Advisory Details (2)

Auto-updated Aug 21, 2026
Patch available. Sources: github_commit, github.
GitHub advisoryMentions a patch (unverified)

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 / EcosystemFix (by version range) / PatchReleasedSource
ubuntulibvncserver1 (0.9.14+dfsg-1ubuntu0.2) @ noble2026-10-12ubuntu

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 rangeFix by version rangeDependents
libvncserver0.9.14+dfsg-1, 0.9.14+dfsg-1+deb12u1
  • every version up to 0.9.14+dfsg-1+deb12u2: fixed in 0.9.14+dfsg-1+deb12u2
—
Debian:13(1)
PackageVulnerable rangeFix by version rangeDependents
libvncserver0.9.15+dfsg-1, 0.9.15+dfsg-1+deb13u1
  • every version up to 0.9.15+dfsg-1+deb13u2: fixed in 0.9.15+dfsg-1+deb13u2
—
Debian:14(1)
PackageVulnerable rangeFix by version rangeDependents
libvncserver0.9.15+dfsg-1, 0.9.15+dfsg-2, 0.9.15+dfsg-3, 0.9.15+dfsg-4, 0.9.15+dfsg-5
  • every version up to 0.9.15+dfsg-6: fixed in 0.9.15+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 15× in last 7d / 98× in last 30d)

Each row is a time one of our pipelines fetched, updated or re-scored this CVE. 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. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.

Showing the most recent 100 of 178 refreshes on record for this CVE.

A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. None are among the latest 100 rows. The 78 oldest rows on record are not shown and were not checked, so the counts can still include repeats.

  1. 2026-10-13 16:34 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  2. 2026-10-12 16:34 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  3. 2026-10-12 16:30 UTCVendor advisory
  4. 2026-10-12 15:59 UTCEG score recompute
  5. 2026-10-11 19:42 UTCEG score recompute
  6. 2026-10-11 16:57 UTCEG score recompute
  7. 2026-10-11 14:20 UTCEG score recompute
  8. 2026-10-11 13:49 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  9. 2026-10-10 20:00 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  10. 2026-10-09 20:07 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  11. 2026-10-09 05:39 UTCEG score recompute
  12. 2026-10-09 05:39 UTCVendor advisory
  13. 2026-10-08 17:12 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  14. 2026-10-08 04:50 UTCEG score recompute
  15. 2026-10-07 23:48 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  16. 2026-10-07 05:55 UTCVendor advisory
  17. 2026-10-06 18:51 UTCEG score recompute
  18. 2026-10-06 18:51 UTCVendor advisory
  19. 2026-10-06 15:18 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  20. 2026-10-06 07:48 UTCEG score recompute
  21. 2026-10-06 07:48 UTCVendor advisory
  22. 2026-10-05 17:43 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  23. 2026-10-05 17:05 UTCVendor advisory
  24. 2026-10-05 04:54 UTCEG score recompute
  25. 2026-10-05 04:54 UTCVendor advisory
Show 75 more
  1. 2026-10-04 23:22 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  2. 2026-10-04 16:13 UTCVendor advisory
  3. 2026-10-04 05:03 UTCVendor advisory
  4. 2026-10-03 17:33 UTCEG score recompute
  5. 2026-10-03 17:33 UTCVendor advisory
  6. 2026-10-03 14:26 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  7. 2026-10-03 06:31 UTCVendor advisory
  8. 2026-10-02 19:28 UTCEG score recompute
  9. 2026-10-02 19:28 UTCVendor advisory
  10. 2026-10-02 17:56 UTCEPSS rescoreEPSS 0.4% · 32nd percentile
  11. 2026-10-02 08:26 UTCVendor advisory
  12. 2026-10-01 21:24 UTCEG score recompute
  13. 2026-10-01 21:24 UTCVendor advisory
  14. 2026-10-01 19:50 UTCEPSS rescoreEPSS 0.6% · 47th percentile
  15. 2026-10-01 07:06 UTCVendor advisory
  16. 2026-09-30 20:02 UTCEG score recompute
  17. 2026-09-30 20:02 UTCVendor advisory
  18. 2026-09-30 15:03 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  19. 2026-09-30 07:48 UTCVendor advisory
  20. 2026-09-29 15:36 UTCEG score recompute
  21. 2026-09-29 15:36 UTCVendor advisory
  22. 2026-09-29 00:04 UTCEG score recompute
  23. 2026-09-29 00:04 UTCVendor advisory
  24. 2026-09-28 13:51 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  25. 2026-09-28 13:02 UTCVendor advisory
  26. 2026-09-28 01:59 UTCVendor advisory
  27. 2026-09-27 14:39 UTCEG score recompute
  28. 2026-09-27 14:39 UTCVendor advisory
  29. 2026-09-27 13:48 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  30. 2026-09-27 02:24 UTCEG score recompute
  31. 2026-09-27 02:24 UTCVendor advisory
  32. 2026-09-26 15:59 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  33. 2026-09-26 00:27 UTCEPSS rescoreEPSS 0.6% · 46th percentile
  34. 2026-09-25 07:04 UTCVendor advisory
  35. 2026-09-24 20:00 UTCEG score recompute
  36. 2026-09-24 20:00 UTCVendor advisory
  37. 2026-09-24 08:53 UTCVendor advisory
  38. 2026-09-23 21:51 UTCEG score recompute
  39. 2026-09-23 21:51 UTCVendor advisory
  40. 2026-09-23 17:53 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  41. 2026-09-23 10:49 UTCVendor advisory
  42. 2026-09-22 23:42 UTCEG score recompute
  43. 2026-09-22 23:42 UTCVendor advisory
  44. 2026-09-22 12:25 UTCVendor advisory
  45. 2026-09-22 01:21 UTCEG score recompute
  46. 2026-09-22 01:21 UTCVendor advisory
  47. 2026-09-21 14:19 UTCVendor advisory
  48. 2026-09-21 03:17 UTCEG score recompute
  49. 2026-09-21 03:17 UTCVendor advisory
  50. 2026-09-20 20:16 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  51. 2026-09-20 16:11 UTCVendor advisory
  52. 2026-09-20 04:58 UTCVendor advisory
  53. 2026-09-19 17:54 UTCEG score recompute
  54. 2026-09-19 17:54 UTCVendor advisory
  55. 2026-09-19 06:52 UTCVendor advisory
  56. 2026-09-18 19:45 UTCEG score recompute
  57. 2026-09-18 19:45 UTCVendor advisory
  58. 2026-09-18 19:28 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  59. 2026-09-18 08:42 UTCVendor advisory
  60. 2026-09-17 21:40 UTCEG score recompute
  61. 2026-09-17 21:40 UTCVendor advisory
  62. 2026-09-17 10:36 UTCVendor advisory
  63. 2026-09-16 23:33 UTCEG score recompute
  64. 2026-09-16 23:33 UTCVendor advisory
  65. 2026-09-16 14:08 UTCEPSS rescoreEPSS 0.3% · 25th percentile
  66. 2026-09-16 12:31 UTCEG score recompute
  67. 2026-09-16 12:31 UTCVendor advisory
  68. 2026-09-16 05:15 UTCEPSS rescoreEPSS 0.3% · 24th percentile
  69. 2026-09-16 01:28 UTCVendor advisory
  70. 2026-09-15 14:26 UTCVendor advisory
  71. 2026-09-15 03:23 UTCEG score recompute
  72. 2026-09-15 03:23 UTCVendor advisory
  73. 2026-09-14 16:21 UTCVendor advisory
  74. 2026-09-14 05:17 UTCVendor advisory
  75. 2026-09-13 18:15 UTCEG score recompute

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Frequently asked(5)

What is CVE-2026-50538?
CVE-2026-50538 is a high-severity vulnerability; its CVE record was 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 the CVE record for CVE-2026-50538 published?
The CVE record for CVE-2026-50538 was published on August 21, 2026. That is the record's publication date; the vulnerability itself may have been made public earlier. EchelonGraph's copy of the record carries a last-modified date of October 12, 2026; the record at its source may have been updated since.
Is CVE-2026-50538 actively exploited?
CVE-2026-50538 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0.4% probability of exploitation in the next 30 days (32nd percentile of EPSS-scored CVEs).
What is the CVSS score of CVE-2026-50538?
CVE-2026-50538 has a CVSS base score of 8.8 (a secondary CVSS source that NVD displays; NVD's own analysis pending).
How do I remediate CVE-2026-50538?
A fix for CVE-2026-50538 is available: update to the fixed version the vendor names in its advisory.

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