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Vulnerability Details :

CVE-2026-33020

Summary
Assigner-GitHub_M
Assigner Org ID-a0819718-46f1-4df5-94e2-005712e83aaa
Published At-14 Apr, 2026 | 21:53
Updated At-15 Apr, 2026 | 13:30
Rejected At-
Credits

libsixel: Integer Overflow in write_png_to_file() leads to Heap-based Buffer Overflow

libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain an integer overflow which leads to a heap buffer overflow via sixel_frame_convert_to_rgb888() in frame.c, where allocation size and pointer offset computations for palettised images (PAL1, PAL2, PAL4) are performed using int arithmetic before casting to size_t. For images whose pixel count exceeds INT_MAX / 4, the overflow produces an undersized heap allocation for the conversion buffer and a negative pointer offset for the normalization sub-buffer, after which sixel_helper_normalize_pixelformat() writes the full image data starting from the invalid pointer, causing massive heap corruption confirmed by ASAN. An attacker providing a specially crafted large palettised PNG can corrupt the heap of the victim process, resulting in a reliable crash and potential arbitrary code execution. This issue has been fixed in version 1.8.7-r1.

Vendors
-
Not available
Products
-
Metrics (CVSS)
VersionBase scoreBase severityVector
Weaknesses
Attack Patterns
Solution/Workaround
References
HyperlinkResource Type
EPSS History
Score
Latest Score
-
N/A
No data available for selected date range
Percentile
Latest Percentile
-
N/A
No data available for selected date range
Stakeholder-Specific Vulnerability Categorization (SSVC)
â–¼Common Vulnerabilities and Exposures (CVE)
cve.org
Assigner:GitHub_M
Assigner Org ID:a0819718-46f1-4df5-94e2-005712e83aaa
Published At:14 Apr, 2026 | 21:53
Updated At:15 Apr, 2026 | 13:30
Rejected At:
â–¼CVE Numbering Authority (CNA)
libsixel: Integer Overflow in write_png_to_file() leads to Heap-based Buffer Overflow

libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain an integer overflow which leads to a heap buffer overflow via sixel_frame_convert_to_rgb888() in frame.c, where allocation size and pointer offset computations for palettised images (PAL1, PAL2, PAL4) are performed using int arithmetic before casting to size_t. For images whose pixel count exceeds INT_MAX / 4, the overflow produces an undersized heap allocation for the conversion buffer and a negative pointer offset for the normalization sub-buffer, after which sixel_helper_normalize_pixelformat() writes the full image data starting from the invalid pointer, causing massive heap corruption confirmed by ASAN. An attacker providing a specially crafted large palettised PNG can corrupt the heap of the victim process, resulting in a reliable crash and potential arbitrary code execution. This issue has been fixed in version 1.8.7-r1.

Affected Products
Vendor
saitoha
Product
libsixel
Versions
Affected
  • < 1.8.7-r1
Problem Types
TypeCWE IDDescription
CWECWE-122CWE-122: Heap-based Buffer Overflow
CWECWE-190CWE-190: Integer Overflow or Wraparound
Type: CWE
CWE ID: CWE-122
Description: CWE-122: Heap-based Buffer Overflow
Type: CWE
CWE ID: CWE-190
Description: CWE-190: Integer Overflow or Wraparound
Metrics
VersionBase scoreBase severityVector
3.17.1HIGH
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H
Version: 3.1
Base score: 7.1
Base severity: HIGH
Vector:
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H
Metrics Other Info
Impacts
CAPEC IDDescription
Solutions

Configurations

Workarounds

Exploits

Credits

Timeline
EventDate
Replaced By

Rejected Reason

References
HyperlinkResource
https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2p
x_refsource_CONFIRM
https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1
x_refsource_MISC
Hyperlink: https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2p
Resource:
x_refsource_CONFIRM
Hyperlink: https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1
Resource:
x_refsource_MISC
â–¼Authorized Data Publishers (ADP)
CISA ADP Vulnrichment
Affected Products
Metrics
VersionBase scoreBase severityVector
Metrics Other Info
Impacts
CAPEC IDDescription
Solutions

Configurations

Workarounds

Exploits

Credits

Timeline
EventDate
Replaced By

Rejected Reason

References
HyperlinkResource
https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2p
exploit
Hyperlink: https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2p
Resource:
exploit
Information is not available yet
â–¼National Vulnerability Database (NVD)
nvd.nist.gov
Source:security-advisories@github.com
Published At:14 Apr, 2026 | 22:16
Updated At:23 Apr, 2026 | 14:47

libsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. Versions 1.8.7 and prior contain an integer overflow which leads to a heap buffer overflow via sixel_frame_convert_to_rgb888() in frame.c, where allocation size and pointer offset computations for palettised images (PAL1, PAL2, PAL4) are performed using int arithmetic before casting to size_t. For images whose pixel count exceeds INT_MAX / 4, the overflow produces an undersized heap allocation for the conversion buffer and a negative pointer offset for the normalization sub-buffer, after which sixel_helper_normalize_pixelformat() writes the full image data starting from the invalid pointer, causing massive heap corruption confirmed by ASAN. An attacker providing a specially crafted large palettised PNG can corrupt the heap of the victim process, resulting in a reliable crash and potential arbitrary code execution. This issue has been fixed in version 1.8.7-r1.

CISA Catalog
Date AddedDue DateVulnerability NameRequired Action
N/A
Date Added: N/A
Due Date: N/A
Vulnerability Name: N/A
Required Action: N/A
Metrics
TypeVersionBase scoreBase severityVector
Secondary3.17.1HIGH
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H
Type: Secondary
Version: 3.1
Base score: 7.1
Base severity: HIGH
Vector:
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H
CPE Matches

saitoha
saitoha
>>libsixel>>Versions before 1.8.7-r1(exclusive)
cpe:2.3:a:saitoha:libsixel:*:*:*:*:*:*:*:*
Weaknesses
CWE IDTypeSource
CWE-122Secondarysecurity-advisories@github.com
CWE-190Secondarysecurity-advisories@github.com
CWE ID: CWE-122
Type: Secondary
Source: security-advisories@github.com
CWE ID: CWE-190
Type: Secondary
Source: security-advisories@github.com
Evaluator Description

Evaluator Impact

Evaluator Solution

Vendor Statements

References
HyperlinkSourceResource
https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1security-advisories@github.com
Release Notes
https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2psecurity-advisories@github.com
Exploit
Vendor Advisory
https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2p134c704f-9b21-4f2e-91b3-4a467353bcc0
Exploit
Vendor Advisory
Hyperlink: https://github.com/saitoha/libsixel/releases/tag/v1.8.7-r1
Source: security-advisories@github.com
Resource:
Release Notes
Hyperlink: https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2p
Source: security-advisories@github.com
Resource:
Exploit
Vendor Advisory
Hyperlink: https://github.com/saitoha/libsixel/security/advisories/GHSA-2xgm-4x47-2x2p
Source: 134c704f-9b21-4f2e-91b3-4a467353bcc0
Resource:
Exploit
Vendor Advisory

Change History

0
Information is not available yet

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Details not found