How severe is CVE-2026-33021?

CVE-2026-33021 has a CVSS 3.x base score of 7.3, rated high severity. It is exploitable over local access with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability high.

Is CVE-2026-33021 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (16th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-33021?

CVE-2026-33021 affects Saitoha Libsixel. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-33021?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

Does CVE-2026-33021 have an EU (EUVD) identifier?

Yes. CVE-2026-33021 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-22746.

When was CVE-2026-33021 published?

CVE-2026-33021 was published on 2026-04-14 and last updated on 2026-06-17.

CVE-2026-33021

CVE-2026-33021 is a high-severity vulnerability in Saitoha Libsixel with a CVSS 3.x base score of 7.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-416.

Key facts

Severity: High (CVSS 3.x base score 7.3)
EPSS exploit prediction: 0% (16th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-22746
Weakness: CWE-416
Affected product: Saitoha Libsixel
Published: 2026-04-14
Last modified: 2026-06-17

Description

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.

Frequently asked questions

What is CVE-2026-33021?: 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.
How severe is CVE-2026-33021?: CVE-2026-33021 has a CVSS 3.x base score of 7.3, rated high severity. It is exploitable over local access with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability high.
Is CVE-2026-33021 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (16th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-33021?: CVE-2026-33021 affects Saitoha Libsixel. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-33021?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
Does CVE-2026-33021 have an EU (EUVD) identifier?: Yes. CVE-2026-33021 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-22746.
When was CVE-2026-33021 published?: CVE-2026-33021 was published on 2026-04-14 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:saitoha:libsixel:*:*:*:*:*:*:*:*

More vulnerabilities in Saitoha Libsixel

CVE-2019-19638 — Critical (CVSS 9.8): An issue was discovered in libsixel 1.8.2. There is a heap-based buffer overflow in the function load_pnm at frompnm.c,…
CVE-2019-19637 — Critical (CVSS 9.8): An issue was discovered in libsixel 1.8.2. There is an integer overflow in the function sixel_decode_raw_impl at…
CVE-2019-19636 — Critical (CVSS 9.8): An issue was discovered in libsixel 1.8.2. There is an integer overflow in the function sixel_encode_body at tosixel.c.
CVE-2019-19635 — Critical (CVSS 9.8): An issue was discovered in libsixel 1.8.2. There is a heap-based buffer overflow in the function sixel_decode_raw_impl…
CVE-2022-27046 — High (CVSS 8.8): libsixel 1.8.6 suffers from a Heap Use After Free vulnerability in in libsixel/src/dither.c:388.
CVE-2022-27044 — High (CVSS 8.8): libsixel 1.8.6 is affected by Buffer Overflow in libsixel/src/quant.c:876.

All CVEs affecting Saitoha Libsixel →

Other CWE-416 (Use After Free) vulnerabilities

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CVE-2026-4688 — Critical (CVSS 10.0): Sandbox escape due to use-after-free in the Disability Access APIs component. This vulnerability was fixed in Firefox…
CVE-2025-24085 — Critical (CVSS 10.0): A use after free issue was addressed with improved memory management. This issue is fixed in iOS 18.3 and iPadOS 18.3,…
CVE-2024-43102 — Critical (CVSS 10.0): Concurrent removals of certain anonymous shared memory mappings by using the UMTX_SHM_DESTROY sub-request of…
CVE-2021-32495 — Critical (CVSS 10.0): Radare2 has a use-after-free vulnerability in pyc parser's get_none_object function. Attacker can read freed memory…

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