Highly exploitable, CVE-2026-33023 poses a critical security risk that could lead to severe breaches.
Status: Received on 14 Apr 2026, 23:16 UTC
Published on: 14 Apr 2026, 23:16 UTC
CVSS Release: version 3
security-advisories@github.com
Secondary
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CVE-2026-33023: libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. In versions 1.8.7 and prior, when built with the --with-gdk-pixbuf2 option, a use-after-free vulnerability exists in load_with_gdkpixbuf() in loader.c. The cleanup path manually frees the sixel_frame_t object and its internal buffers without consulting the reference count, even though the object was created via the refcounted constructor sixel_frame_new() and exposed to the public callback. A callback that calls sixel_frame_ref(frame) to retain a logically valid reference will hold a dangling pointer after sixel_helper_load_image_file() returns, and any subsequent access to the frame or its fields triggers a use-after-free confirmed by AddressSanitizer. The root cause is a consistency failure between two cleanup strategies in the same codebase: sixel_frame_unref() is used in load_with_builtin() but raw free() is used in load_with_gdkpixbuf(). An attacker supplying a crafted image to any application built against libsixel with gdk-pixbuf2 support can trigger this reliably, potentially leading to information disclosure, memory corruption, or code execution. This issue has been fixed in version 1.8.7-r1.
The exploitability of CVE-2026-33023 depends on two key factors: attack complexity (the level of effort required to execute an exploit) and privileges required (the access level an attacker needs).
With low attack complexity and no required privileges, CVE-2026-33023 is an easy target for cybercriminals. Organizations should prioritize immediate mitigation measures to prevent unauthorized access and data breaches.
A lower complexity and fewer privilege requirements make exploitation easier. Security teams should evaluate these aspects to determine the urgency of mitigation strategies, such as patch management and access control policies.
Attack Complexity (AC) measures the difficulty in executing an exploit. A high AC means that specific conditions must be met, making an attack more challenging, while a low AC means the vulnerability can be exploited with minimal effort.
Privileges Required (PR) determine the level of system access necessary for an attack. Vulnerabilities requiring no privileges are more accessible to attackers, whereas high privilege requirements limit exploitation to authorized users with elevated access.
Above is the CVSS Sub-score Breakdown for CVE-2026-33023, illustrating how Base, Impact, and Exploitability factors combine to form the overall severity rating. A higher sub-score typically indicates a more severe or easier-to-exploit vulnerability.
Below is the Impact Analysis for CVE-2026-33023, showing how Confidentiality, Integrity, and Availability might be affected if the vulnerability is exploited. Higher values usually signal greater potential damage.
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