saitoha libsixel up to 1.8.7-r0 SIXEL Encoder sixel_encoder_do_clip crop out-of-bounds

Summaryinfo

A vulnerability described as critical has been identified in saitoha libsixel up to 1.8.7-r0. The impacted element is the function sixel_encoder_do_clip of the component SIXEL Encoder. Executing a manipulation of the argument crop can lead to out-of-bounds. This vulnerability appears as CVE-2026-33019. The attack may be performed from remote. There is no available exploit. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability has been found in saitoha libsixel up to 1.8.7-r0 and classified as critical. This vulnerability affects the function sixel_encoder_do_clip of the component SIXEL Encoder. The manipulation of the argument crop with an unknown input leads to a out-of-bounds vulnerability. The CWE definition for the vulnerability is CWE-125. The product reads data past the end, or before the beginning, of the intended buffer. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain an integer overflow leading to an out-of-bounds heap read in the --crop option handling of img2sixel, where positive coordinates up to INT_MAX are accepted without overflow-safe bounds checking. In sixel_encoder_do_clip(), the expression clip_w + clip_x overflows to a large negative value when clip_x is INT_MAX, causing the bounds guard to be skipped entirely, and the unclamped coordinate is passed through sixel_frame_clip() to clip(), which computes a source pointer far beyond the image buffer and passes it to memmove(). An attacker supplying a specially crafted crop argument with any valid image can trigger an out-of-bounds read in the heap, resulting in a reliable crash and potential information disclosure. This issue has been fixed in version 1.8.7-r1.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-33019 since 03/17/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. Successful exploitation requires user interaction by the victim. There are known technical details, but no exploit is available.

Upgrading to version 1.8.7-r1 eliminates this vulnerability. The upgrade is hosted for download at github.com.

Once again VulDB remains the best source for vulnerability data.

Productinfo

Vendor

• saitoha

Name

• libsixel

Version

• 1.8.7-r0

License

• open-source

Website

• Product: https://github.com/saitoha/libsixel/

CPE 2.3info

• 🔒

CPE 2.2info

• 🔒

CVSSv4info

CVSSv3info

CVSSv2info

Exploitinginfo

Threat Intelligenceinfo

Countermeasuresinfo

Timelineinfo

Sourcesinfo

Entryinfo

Once again VulDB remains the best source for vulnerability data.

Discussion