{"id":"CVE-2026-50538","state":"PUBLISHED","title":"libvncclient Tight decoder has an attacker-controlled heap out-of-bounds write","description":"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\nis 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.","publishedAt":"2026-08-21T21:03:58.147Z","updatedAt":"2026-08-24T19:39:57.811Z","severity":{"score":8.8,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","source":"GitHub_M"},"assigner":"GitHub_M","products":["LibVNC libvncserver"],"affected":[{"vendor":"LibVNC","product":"libvncserver","versions":[{"version":">= 0.9.12, <= 0.9.15","status":"affected"}]}],"references":["https://github.com/LibVNC/libvncserver/security/advisories/GHSA-v9pm-47h4-jcq8","https://github.com/LibVNC/libvncserver/commit/540332be3e0acc566fa64da6f1b4680c72c724dd"],"weaknesses":["CWE-122","CWE-787"],"ingestedAt":"2026-10-29T20:12:16.098Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/50xxx/CVE-2026-50538.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-50538","state":"PUBLISHED","datePublished":"2026-08-21T21:03:58.147Z","dateUpdated":"2026-08-24T19:39:57.811Z","assignerShortName":"GitHub_M","assignerOrgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateReserved":"2026-06-04T20:37:18.653Z"},"containers":{"cna":{"title":"libvncclient Tight decoder has an attacker-controlled heap out-of-bounds write","descriptions":[{"lang":"en","value":"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\nis 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."}],"affected":[{"vendor":"LibVNC","product":"libvncserver","versions":[{"version":">= 0.9.12, <= 0.9.15","status":"affected"}]}],"references":[{"url":"https://github.com/LibVNC/libvncserver/security/advisories/GHSA-v9pm-47h4-jcq8","name":"https://github.com/LibVNC/libvncserver/security/advisories/GHSA-v9pm-47h4-jcq8","tags":["x_refsource_CONFIRM"]},{"url":"https://github.com/LibVNC/libvncserver/commit/540332be3e0acc566fa64da6f1b4680c72c724dd","name":"https://github.com/LibVNC/libvncserver/commit/540332be3e0acc566fa64da6f1b4680c72c724dd","tags":["x_refsource_MISC"]}],"metrics":[{"cvssV3_1":{"attackComplexity":"LOW","attackVector":"NETWORK","availabilityImpact":"HIGH","baseScore":8.8,"baseSeverity":"HIGH","confidentialityImpact":"HIGH","integrityImpact":"HIGH","privilegesRequired":"NONE","scope":"UNCHANGED","userInteraction":"REQUIRED","vectorString":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H","version":"3.1"}}],"problemTypes":[{"descriptions":[{"cweId":"CWE-122","lang":"en","description":"CWE-122: Heap-based Buffer Overflow","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-787","lang":"en","description":"CWE-787: Out-of-bounds Write","type":"CWE"}]}],"providerMetadata":{"shortName":"GitHub_M","orgId":"a0819718-46f1-4df5-94e2-005712e83aaa","dateUpdated":"2026-08-21T21:03:58.147Z"},"source":{"advisory":"GHSA-v9pm-47h4-jcq8","discovery":"UNKNOWN"}},"adp":[{"title":"CISA ADP Vulnrichment","references":[{"url":"https://github.com/LibVNC/libvncserver/security/advisories/GHSA-v9pm-47h4-jcq8","tags":["exploit"]}],"metrics":[{"other":{"type":"ssvc","content":{"timestamp":"2026-08-24T19:39:31.246844Z","id":"CVE-2026-50538","options":[{"Exploitation":"poc"},{"Automatable":"no"},{"Technical Impact":"total"}],"role":"CISA Coordinator","version":"2.0.3"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-08-24T19:39:57.811Z"}}]}}}