FKIE_CVE-2026-33020

Vulnerability from fkie_nvd - Published: 2026-04-14 22:16 - Updated: 2026-07-25 11:10
Severity
7.1 (High) - CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H
Summary
libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain an integer overflow which leads to a heap buffer overflow via sixel_frame_convert_to_rgb888() in frame.c, where allocation size and pointer offset computations for palettised images (PAL1, PAL2, PAL4) are performed using int arithmetic before casting to size_t. For images whose pixel count exceeds INT_MAX / 4, the overflow produces an undersized heap allocation for the conversion buffer and a negative pointer offset for the normalization sub-buffer, after which sixel_helper_normalize_pixelformat() writes the full image data starting from the invalid pointer, causing massive heap corruption confirmed by ASAN. An attacker providing a specially crafted large palettised PNG can corrupt the heap of the victim process, resulting in a reliable crash and potential arbitrary code execution. This issue has been fixed in version 1.8.7-r1.
References
security-advisories@github.comhttps://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1Release Notes
security-advisories@github.comhttps://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2pExploit, Vendor Advisory
134c704f-9b21-4f2e-91b3-4a467353bcc0https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2pExploit, Vendor Advisory
Impacted products
Vendor Product Version
saitoha libsixel *
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "product": "libsixel",
          "vendor": "saitoha",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 1.8.7-r1"
            }
          ]
        }
      ],
      "source": "security-advisories@github.com"
    }
  ],
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:saitoha:libsixel:*:*:*:*:*:*:*:*",
              "matchCriteriaId": "E16EAA6A-544F-4D16-829D-1B7C9979EA6A",
              "versionEndExcluding": "1.8.7-r1",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "libsixel is a SIXEL encoder/decoder implementation derived from kmiya\u0027s sixel. Versions 1.8.7 and prior contain an integer overflow which leads to a heap buffer overflow via sixel_frame_convert_to_rgb888() in frame.c, where allocation size and pointer offset computations for palettised images (PAL1, PAL2, PAL4) are performed using int arithmetic before casting to size_t. For images whose pixel count exceeds INT_MAX / 4, the overflow produces an undersized heap allocation for the conversion buffer and a negative pointer offset for the normalization sub-buffer, after which sixel_helper_normalize_pixelformat() writes the full image data starting from the invalid pointer, causing massive heap corruption confirmed by ASAN. An attacker providing a specially crafted large palettised PNG can corrupt the heap of the victim process, resulting in a reliable crash and potential arbitrary code execution.\nThis issue has been fixed in version 1.8.7-r1."
    },
    {
      "lang": "es",
      "value": "libsixel es una implementaci\u00f3n de codificador/decodificador SIXEL derivada de sixel de kmiya. Las versiones 1.8.7 y anteriores contienen un desbordamiento de entero que conduce a un desbordamiento de b\u00fafer de mont\u00f3n a trav\u00e9s de sixel_frame_convert_to_rgb888() en frame.c, donde los c\u00e1lculos de tama\u00f1o de asignaci\u00f3n y desplazamiento de puntero para im\u00e1genes paletizadas (PAL1, PAL2, PAL4) se realizan utilizando aritm\u00e9tica de enteros antes de la conversi\u00f3n a size_t. Para im\u00e1genes cuyo recuento de p\u00edxeles excede INT_MAX / 4, el desbordamiento produce una asignaci\u00f3n de mont\u00f3n de tama\u00f1o insuficiente para el b\u00fafer de conversi\u00f3n y un desplazamiento de puntero negativo para el sub-b\u00fafer de normalizaci\u00f3n, despu\u00e9s de lo cual sixel_helper_normalize_pixelformat() escribe los datos completos de la imagen comenzando desde el puntero inv\u00e1lido, causando una corrupci\u00f3n masiva del mont\u00f3n confirmada por ASAN. Un atacante que proporciona un PNG paletizado grande especialmente dise\u00f1ado puede corromper el mont\u00f3n del proceso v\u00edctima, lo que resulta en un fallo fiable y una potencial ejecuci\u00f3n de c\u00f3digo arbitrario. Este problema ha sido solucionado en la versi\u00f3n 1.8.7-r1."
    }
  ],
  "id": "CVE-2026-33020",
  "lastModified": "2026-07-25T11:10:00.100",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "HIGH",
          "baseScore": 7.1,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "NONE",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 1.8,
        "impactScore": 5.2,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-33020",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "no"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-04-15T13:30:43.489988Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-04-14T22:16:30.543",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Release Notes"
      ],
      "url": "https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2p"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "tags": [
        "Exploit",
        "Vendor Advisory"
      ],
      "url": "https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2p"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-122"
        },
        {
          "lang": "en",
          "value": "CWE-190"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}



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