CVE-2026-33020: CWE-122: Heap-based Buffer Overflow in saitoha libsixel
libsixel versions prior to 1. 8. 7-r1 contain a heap-based buffer overflow vulnerability caused by an integer overflow in the sixel_frame_convert_to_rgb888() function. This overflow leads to an undersized heap allocation and invalid pointer arithmetic when processing large palettised images, resulting in heap corruption. An attacker can exploit this by supplying a specially crafted large palettised PNG file, potentially causing a crash or arbitrary code execution. The issue is fixed in version 1. 8. 7-r1.
AI Analysis
Technical Summary
The vulnerability in saitoha libsixel (CVE-2026-33020) arises from an integer overflow in the sixel_frame_convert_to_rgb888() function within frame.c. The function uses int arithmetic for allocation size and pointer offset calculations for palettised images, which can overflow when the pixel count exceeds INT_MAX / 4. This overflow causes an undersized heap allocation and a negative pointer offset, leading to heap corruption when sixel_helper_normalize_pixelformat() writes image data starting from the invalid pointer. This can be triggered by a crafted large palettised PNG image, enabling reliable crashes and potential arbitrary code execution. The vulnerability affects versions prior to 1.8.7-r1, where it has been fixed.
Potential Impact
Exploitation of this vulnerability allows an attacker to corrupt the heap of the victim process by providing a specially crafted large palettised PNG image. This can result in a reliable denial of service (crash) and may lead to arbitrary code execution within the context of the affected application. The CVSS score of 7.1 reflects high severity with high impact on integrity and availability, requiring user interaction but no privileges.
Mitigation Recommendations
This vulnerability has been fixed in libsixel version 1.8.7-r1. Users and administrators should upgrade to version 1.8.7-r1 or later to remediate this issue. No other mitigation or workaround is specified. Patch status is confirmed by the vendor's fix in 1.8.7-r1.
CVE-2026-33020: CWE-122: Heap-based Buffer Overflow in saitoha libsixel
Description
libsixel versions prior to 1. 8. 7-r1 contain a heap-based buffer overflow vulnerability caused by an integer overflow in the sixel_frame_convert_to_rgb888() function. This overflow leads to an undersized heap allocation and invalid pointer arithmetic when processing large palettised images, resulting in heap corruption. An attacker can exploit this by supplying a specially crafted large palettised PNG file, potentially causing a crash or arbitrary code execution. The issue is fixed in version 1. 8. 7-r1.
CVSS v3.1
Score 7.1high
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
The vulnerability in saitoha libsixel (CVE-2026-33020) arises from an integer overflow in the sixel_frame_convert_to_rgb888() function within frame.c. The function uses int arithmetic for allocation size and pointer offset calculations for palettised images, which can overflow when the pixel count exceeds INT_MAX / 4. This overflow causes an undersized heap allocation and a negative pointer offset, leading to heap corruption when sixel_helper_normalize_pixelformat() writes image data starting from the invalid pointer. This can be triggered by a crafted large palettised PNG image, enabling reliable crashes and potential arbitrary code execution. The vulnerability affects versions prior to 1.8.7-r1, where it has been fixed.
Potential Impact
Exploitation of this vulnerability allows an attacker to corrupt the heap of the victim process by providing a specially crafted large palettised PNG image. This can result in a reliable denial of service (crash) and may lead to arbitrary code execution within the context of the affected application. The CVSS score of 7.1 reflects high severity with high impact on integrity and availability, requiring user interaction but no privileges.
Mitigation Recommendations
This vulnerability has been fixed in libsixel version 1.8.7-r1. Users and administrators should upgrade to version 1.8.7-r1 or later to remediate this issue. No other mitigation or workaround is specified. Patch status is confirmed by the vendor's fix in 1.8.7-r1.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- GitHub_M
- Date Reserved
- 2026-03-17T17:22:14.667Z
- Cvss Version
- 3.1
- State
- PUBLISHED
- Remediation Level
- null
Threat ID: 69deb96d82d89c981f0b1a11
Added to database: 4/14/2026, 10:02:21 PM
Last enriched: 4/22/2026, 6:49:59 AM
Last updated: 5/30/2026, 1:28:29 AM
Views: 83
Community Reviews
0 reviewsCrowdsource mitigation strategies, share intel context, and vote on the most helpful responses. Sign in to add your voice and help keep defenders ahead.
Want to contribute mitigation steps or threat intel context? Sign in or create an account to join the community discussion.
Actions
Updates to AI analysis require Pro Console access. Upgrade inside Console → Billing.
Need more coverage?
Upgrade to Pro Console for AI refresh and higher limits.
For incident response and remediation, OffSeq services can help resolve threats faster.
Latest Threats
Check if your credentials are on the dark web
Instant breach scanning across billions of leaked records. Free tier available.