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DEBIAN-CVE-2026-33020

Type: advisorySource: OSV1 source record

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.

Announced Source revision 1
Original source ↗

DEBIAN-CVE-2026-33020

Primary source · Revision 1

Imported from structured advisory data. Source references identify upstream records or fields; verify affected versions and your deployed configuration.

Security context

Source reference: osv:DEBIAN-CVE-2026-33020

libsixel

Source reference: /affected/0/package/name

Affected versions
1.10.3-3

Source reference: /affected/0/versions

1.10.5-1

Source reference: /affected/0/versions

1:1.8.7-1

Source reference: /affected/0/versions

1:1.8.7-2

Source reference: /affected/0/versions

1:1.8.7-3

Source reference: /affected/0/versions

1:1.8.7-4

Source reference: /affected/0/versions

1:1.8.7-5

Source reference: /affected/0/versions

1:1.8.7-6

Source reference: /affected/0/versions

1:1.8.7-r2-1

Source reference: /affected/0/versions

Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

libsixel

Source reference: /affected/1/package/name

Affected versions
1.10.5-1

Source reference: /affected/1/versions

1:1.8.7-1

Source reference: /affected/1/versions

1:1.8.7-2

Source reference: /affected/1/versions

1:1.8.7-3

Source reference: /affected/1/versions

1:1.8.7-4

Source reference: /affected/1/versions

1:1.8.7-5

Source reference: /affected/1/versions

1:1.8.7-6

Source reference: /affected/1/versions

1:1.8.7-r2-1

Source reference: /affected/1/versions

Fixed versions
Not stated in this record
Prerequisites
Not stated in this record

libsixel

Source reference: /affected/2/package/name

Affected versions
1.10.5-1

Source reference: /affected/2/versions

1:1.8.7-1

Source reference: /affected/2/versions

1:1.8.7-2

Source reference: /affected/2/versions

1:1.8.7-3

Source reference: /affected/2/versions

1:1.8.7-4

Source reference: /affected/2/versions

1:1.8.7-5

Source reference: /affected/2/versions

1:1.8.7-6

Source reference: /affected/2/versions

Fixed versions
1:1.8.7-r2-1

Source reference: /affected/2/ranges

Prerequisites
Not stated in this record

Structured affected-version data

Original package identities and version rules from this source.

[
  {
    "ranges": [
      {
        "type": "ECOSYSTEM",
        "events": [
          {
            "introduced": "0"
          }
        ]
      }
    ],
    "package": {
      "name": "libsixel",
      "purl": "pkg:deb/debian/libsixel?arch=source&distro=bookworm",
      "ecosystem": "Debian:12"
    },
    "versions": [
      "1.10.3-3",
      "1.10.5-1",
      "1:1.8.7-1",
      "1:1.8.7-2",
      "1:1.8.7-3",
      "1:1.8.7-4",
      "1:1.8.7-5",
      "1:1.8.7-6",
      "1:1.8.7-r2-1"
    ],
    "database_specific": {
      "source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-33020.json"
    },
    "ecosystem_specific": {
      "urgency": "not yet assigned"
    }
  },
  {
    "ranges": [
      {
        "type": "ECOSYSTEM",
        "events": [
          {
            "introduced": "0"
          }
        ]
      }
    ],
    "package": {
      "name": "libsixel",
      "purl": "pkg:deb/debian/libsixel?arch=source&distro=trixie",
      "ecosystem": "Debian:13"
    },
    "versions": [
      "1.10.5-1",
      "1:1.8.7-1",
      "1:1.8.7-2",
      "1:1.8.7-3",
      "1:1.8.7-4",
      "1:1.8.7-5",
      "1:1.8.7-6",
      "1:1.8.7-r2-1"
    ],
    "database_specific": {
      "source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-33020.json"
    },
    "ecosystem_specific": {
      "urgency": "not yet assigned"
    }
  },
  {
    "ranges": [
      {
        "type": "ECOSYSTEM",
        "events": [
          {
            "introduced": "0"
          },
          {
            "fixed": "1:1.8.7-r2-1"
          }
        ]
      }
    ],
    "package": {
      "name": "libsixel",
      "purl": "pkg:deb/debian/libsixel?arch=source&distro=forky",
      "ecosystem": "Debian:14"
    },
    "versions": [
      "1.10.5-1",
      "1:1.8.7-1",
      "1:1.8.7-2",
      "1:1.8.7-3",
      "1:1.8.7-4",
      "1:1.8.7-5",
      "1:1.8.7-6"
    ],
    "database_specific": {
      "source": "https://storage.googleapis.com/debian-osv/debian-cve-osv/DEBIAN-CVE-2026-33020.json"
    },
    "ecosystem_specific": {
      "urgency": "not yet assigned"
    }
  }
]

Publisher severity

No explicit severity was provided.

Event
#56760 · Revision 1
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Publisher date
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