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Vulnerabilities

Vulnerability · CVE-2026-33020

libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel.

Published Apr 14, 2026 · catalog updated Jul 25, 2026 · libsixel is a SIXEL

Check if you run it

No confirmed exploitation is on record for CVE-2026-33020. EPSS is 0.22%. Act only if a listed version of libsixel is a SIXEL is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (libsixel is a SIXEL).
  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
High7.1
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.22%
Remediation
Advisory link
Affected products
cpe saitoha/libsixel

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe saitoha/libsixelversion unspecified

How to fix CVE-2026-33020

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-33020. EPSS is 0.22%. Act only if a listed version of libsixel is a SIXEL is installed.

Which versions are affected?

Affected version ranges are not on this record. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-122: Heap-based Buffer Overflow; CWE-190: Integer Overflow. EPSS 0.22%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Apr 14, 2026 · NIST NVD

    Detected

    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 cou

  2. Jul 25, 2026 · NIST NVD

    Updated

    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 cou

Sources

  • CVE.orgVulnerability recordCVE-2026-33020

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-33020

    30-day exploitation probability 0.2%

    first.org
  • NIST NVDVulnerability recordCVE-2026-33020

    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 pale

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.