CVE-2026-44988 (GCVE-0-2026-44988)

Vulnerability from cvelistv5 – Published: 2026-05-27 14:26 – Updated: 2026-05-29 15:16
VLAI
Title
LibVNCClient Tight Gradient decoding allows malicious server-triggered heap/stack OOB writes
Summary
LibVNCClient is a library for easy implementation of a VNC client. In 0.9.15 and earlier, LibVNCClient's Tight encoding decoder uses fixed-size 2048-pixel scratch buffers for the Gradient filter, but it does not reject Tight rectangles whose width is larger than 2048 pixels. A malicious VNC server can send a crafted FramebufferUpdate rectangle using Tight encoding with NoZlib | ExplicitFilter and the Gradient filter. When a LibVNCClient-based client connects, the client processes the server-controlled rectangle width and writes beyond fixed-size Gradient buffers. This vulnerability is fixed with commit 5b270544b85233668b98161323297d418a8f5fd1.
Severity
8.8 (High)
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-05-29 03:55 UTC
CWE
Assigner
References
Impacted products
Vendor Product Version CPE status
LibVNC libvncserver Affected: <= 0.9.15
guessed Create a notification for this product.
Show details on NVD website
To clipboard 

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-44988",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-05-29T03:55:55.774539Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-05-29T15:16:13.607Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "libvncserver",
          "vendor": "LibVNC",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c= 0.9.15"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "LibVNCClient is a library for easy implementation of a VNC client. In 0.9.15 and earlier, LibVNCClient\u0027s Tight encoding decoder uses fixed-size 2048-pixel scratch buffers for the Gradient filter, but it does not reject Tight rectangles whose width is larger than 2048 pixels. A malicious VNC server can send a crafted FramebufferUpdate rectangle using Tight encoding with NoZlib | ExplicitFilter and the Gradient filter. When a LibVNCClient-based client connects, the client processes the server-controlled rectangle width and writes beyond fixed-size Gradient buffers. This vulnerability is fixed with commit 5b270544b85233668b98161323297d418a8f5fd1."
        }
      ],
      "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-787",
              "description": "CWE-787: Out-of-bounds Write",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-05-27T14:26:50.063Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/LibVNC/libvncserver/security/advisories/GHSA-jcc5-8wj4-7c58",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/LibVNC/libvncserver/security/advisories/GHSA-jcc5-8wj4-7c58"
        },
        {
          "name": "https://github.com/LibVNC/libvncserver/commit/5b270544b85233668b98161323297d418a8f5fd1",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/LibVNC/libvncserver/commit/5b270544b85233668b98161323297d418a8f5fd1"
        }
      ],
      "source": {
        "advisory": "GHSA-jcc5-8wj4-7c58",
        "discovery": "UNKNOWN"
      },
      "title": "LibVNCClient Tight Gradient decoding allows malicious server-triggered heap/stack OOB writes"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-44988",
    "datePublished": "2026-05-27T14:26:50.063Z",
    "dateReserved": "2026-05-08T16:23:33.265Z",
    "dateUpdated": "2026-05-29T15:16:13.607Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-44988",
      "date": "2026-09-28",
      "epss": "0.00442",
      "percentile": "0.35919"
    },
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "product": "libvncserver",
                "vendor": "LibVNC",
                "versions": [
                  {
                    "status": "affected",
                    "version": "\u003c= 0.9.15"
                  }
                ]
              }
            ],
            "source": "security-advisories@github.com"
          }
        ],
        "cveTags": [],
        "descriptions": [
          {
            "lang": "en",
            "value": "LibVNCClient is a library for easy implementation of a VNC client. In 0.9.15 and earlier, LibVNCClient\u0027s Tight encoding decoder uses fixed-size 2048-pixel scratch buffers for the Gradient filter, but it does not reject Tight rectangles whose width is larger than 2048 pixels. A malicious VNC server can send a crafted FramebufferUpdate rectangle using Tight encoding with NoZlib | ExplicitFilter and the Gradient filter. When a LibVNCClient-based client connects, the client processes the server-controlled rectangle width and writes beyond fixed-size Gradient buffers. This vulnerability is fixed with commit 5b270544b85233668b98161323297d418a8f5fd1."
          }
        ],
        "id": "CVE-2026-44988",
        "lastModified": "2026-06-17T10:51:33.753",
        "metrics": {
          "cvssMetricV31": [
            {
              "cvssData": {
                "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"
              },
              "exploitabilityScore": 2.8,
              "impactScore": 5.9,
              "source": "security-advisories@github.com",
              "type": "Secondary"
            }
          ],
          "ssvcV203": [
            {
              "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "ssvcData": {
                "id": "CVE-2026-44988",
                "options": [
                  {
                    "exploitation": "none"
                  },
                  {
                    "automatable": "no"
                  },
                  {
                    "technicalImpact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-05-29T03:55:55.774539Z",
                "version": "2.0.3"
              }
            }
          ]
        },
        "published": "2026-05-27T15:16:29.830",
        "references": [
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/LibVNC/libvncserver/commit/5b270544b85233668b98161323297d418a8f5fd1"
          },
          {
            "source": "security-advisories@github.com",
            "url": "https://github.com/LibVNC/libvncserver/security/advisories/GHSA-jcc5-8wj4-7c58"
          }
        ],
        "sourceIdentifier": "security-advisories@github.com",
        "vulnStatus": "Awaiting Analysis",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-787"
              }
            ],
            "source": "security-advisories@github.com",
            "type": "Secondary"
          }
        ]
      }
    },
    "redhat_vex": {
      "current_release_date": "2026-06-05T19:12:10+00:00",
      "cve": "CVE-2026-44988",
      "id": "CVE-2026-44988",
      "initial_release_date": "2026-01-01T00:00:00+00:00",
      "product_status:known_not_affected": "1",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "LibVNCClient Tight Gradient decoding allows malicious server-triggered heap/stack OOB writes",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-44988.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-08-27T17:02:18Z",
      "cve": "CVE-2026-44988",
      "id": "CVE-2026-44988",
      "initial_release_date": "2026-05-28T03:57:43Z",
      "product_status:known_affected": "6",
      "product_status:recommended": "34",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-44988",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-44988.json",
      "version": "7"
    },
    "vulnrichment": {
      "containers": {
        "adp": [
          {
            "metrics": [
              {
                "other": {
                  "content": {
                    "id": "CVE-2026-44988",
                    "options": [
                      {
                        "Exploitation": "none"
                      },
                      {
                        "Automatable": "no"
                      },
                      {
                        "Technical Impact": "total"
                      }
                    ],
                    "role": "CISA Coordinator",
                    "timestamp": "2026-05-29T03:55:55.774539Z",
                    "version": "2.0.3"
                  },
                  "type": "ssvc"
                }
              }
            ],
            "providerMetadata": {
              "dateUpdated": "2026-05-28T14:24:40.414Z",
              "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "shortName": "CISA-ADP"
            },
            "title": "CISA ADP Vulnrichment"
          }
        ],
        "cna": {
          "affected": [
            {
              "product": "libvncserver",
              "vendor": "LibVNC",
              "versions": [
                {
                  "status": "affected",
                  "version": "\u003c= 0.9.15"
                }
              ]
            }
          ],
          "descriptions": [
            {
              "lang": "en",
              "value": "LibVNCClient is a library for easy implementation of a VNC client. In 0.9.15 and earlier, LibVNCClient\u0027s Tight encoding decoder uses fixed-size 2048-pixel scratch buffers for the Gradient filter, but it does not reject Tight rectangles whose width is larger than 2048 pixels. A malicious VNC server can send a crafted FramebufferUpdate rectangle using Tight encoding with NoZlib | ExplicitFilter and the Gradient filter. When a LibVNCClient-based client connects, the client processes the server-controlled rectangle width and writes beyond fixed-size Gradient buffers. This vulnerability is fixed with commit 5b270544b85233668b98161323297d418a8f5fd1."
            }
          ],
          "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-787",
                  "description": "CWE-787: Out-of-bounds Write",
                  "lang": "en",
                  "type": "CWE"
                }
              ]
            }
          ],
          "providerMetadata": {
            "dateUpdated": "2026-05-27T14:26:50.063Z",
            "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
            "shortName": "GitHub_M"
          },
          "references": [
            {
              "name": "https://github.com/LibVNC/libvncserver/security/advisories/GHSA-jcc5-8wj4-7c58",
              "tags": [
                "x_refsource_CONFIRM"
              ],
              "url": "https://github.com/LibVNC/libvncserver/security/advisories/GHSA-jcc5-8wj4-7c58"
            },
            {
              "name": "https://github.com/LibVNC/libvncserver/commit/5b270544b85233668b98161323297d418a8f5fd1",
              "tags": [
                "x_refsource_MISC"
              ],
              "url": "https://github.com/LibVNC/libvncserver/commit/5b270544b85233668b98161323297d418a8f5fd1"
            }
          ],
          "source": {
            "advisory": "GHSA-jcc5-8wj4-7c58",
            "discovery": "UNKNOWN"
          },
          "title": "LibVNCClient Tight Gradient decoding allows malicious server-triggered heap/stack OOB writes"
        }
      },
      "cveMetadata": {
        "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "assignerShortName": "GitHub_M",
        "cveId": "CVE-2026-44988",
        "datePublished": "2026-05-27T14:26:50.063Z",
        "dateReserved": "2026-05-08T16:23:33.265Z",
        "dateUpdated": "2026-05-29T15:16:13.607Z",
        "state": "PUBLISHED"
      },
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.