Use After Free Affecting libsixel package, versions *
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-ECHOLATEST-LIBSIXEL-21184811
- published18 Oct 2026
- disclosed14 Apr 2026
Introduced: 14 Apr 2026
CVE-2026-33021 (opens in a new tab)How to fix?
There is no fixed version for Echo:latest libsixel.
NVD Description
Note: Versions mentioned in the description apply only to the upstream libsixel package and not the libsixel package as distributed by Echo.
See How to fix? for Echo:latest relevant fixed versions and status.
libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain a use-after-free vulnerability in sixel_encoder_encode_bytes() because sixel_frame_init() stores the caller-owned pixel buffer pointer directly in frame->pixels without making a defensive copy. When a resize operation is triggered, sixel_frame_convert_to_rgb888() unconditionally frees this caller-owned buffer and replaces it with a new internal allocation, leaving the caller with a dangling pointer. Any subsequent access to the original buffer by the caller constitutes a use-after-free, confirmed by AddressSanitizer. An attacker who controls incoming frames can trigger this bug repeatedly and predictably, resulting in a reliable crash with potential for code execution. This issue has been fixed in version 1.8.7-r1.