CVE-2026-44636
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedlibsixel is a SIXEL encoder/decoder implementation derived from kmiya's sixel. From to 1.8.7-r1, signed integer overflow in sixel_encode_highcolor's allocation size calculation can lead to a heap buffer overflow. The public sixel_encode entry point validates only that width and height are greater than zero, with no upper bound. width and height are multiplied as plain int when computing the allocation size for paletted_pixels and normalized_pixels. Any caller that asks libsixel to encode a pixel buffer with width times height greater than INT_MAX (about 2.15 billion) will hit a wrapped allocation size; under the right wrap, the malloc succeeds with a buffer much smaller than the encoder expects, and the encoder writes past the end of the heap allocation. This vulnerability is fixed in 1.8.7-r2.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceIn libsixel versions up to 1.8.7-r1, the sixel_encode_highcolor function performs width × height multiplication as a plain int to calculate heap allocation size for pixel buffers. When width × height exceeds INT_MAX (~2.15 billion), integer overflow occurs, causing malloc to allocate a much smaller buffer than expected. The encoder then writes past the buffer boundary, resulting in heap buffer overflow. The sixel_encode entry point only validates that dimensions are greater than zero without upper bounds.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data>= 1.4.4, < 1.8.7-r2CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- High
- Availability
- High
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify installed libsixel versionRun 'pkg-config --modversion libsixel' or check the package manager (e.g., 'dpkg -l libsixel', 'rpm -qi libsixel', or check /usr/include/sixel.h for version macros)Affected if version is 1.4.4 or higher but lower than 1.8.7-r2
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Locate libsixel library binaryFind the shared library with 'ldconfig -p | grep sixel' or 'find /usr -name "*libsixel*"' and check its version with 'file' or 'strings'Affected if the installed library version matches the affected range above
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Identify code using sixel_encode or sixel_encode_highcolorSearch source code for calls to sixel_encode, sixel_encode_highcolor, or sixel_encode_gray using 'grep -r "sixel_encode"' in the projectAffected if the application calls either of these functions with image dimensions from untrusted input
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Check dimension bounds in encoder callsReview the code that invokes the encoder to see how width and height parameters are determined; look for user-controlled or file-derived dimensions without upper limit validationAffected if dimensions passed to the encoder can exceed approximately 46340 x 46340 (since 46340^2 approaches INT_MAX) without explicit bounds checking
You are affected if libsixel version 1.4.4 through 1.8.7-r1 is installed AND your code passes image dimensions that could exceed roughly 46340 in either width or height to sixel_encode or sixel_encode_highcolor.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped1.8.7-r2
Upgrade to libsixel version 1.8.7-r2 or later, which includes proper integer overflow validation in the allocation size calculation. Until upgraded, enforce strict upper bounds on image dimensions before passing to libsixel.
libsixel version 1.8.7-r2 or later
- 1. Identify the current installed version of libsixel using your system's package manager (e.g., dpkg -l | grep libsixel, rpm -qa | grep libsixel, orpkg-config --modversion libsixel)
- 2. Remove the vulnerable version of libsixel: On Debian/Ubuntu: sudo apt remove libsixel-dev or sudo apt remove libsixel1; On Red Hat/CentOS: sudo yum remove libsixel-devel
- 3. Update package repositories to ensure latest packages are available: sudo apt update or sudo yum check-update
- 4. Install the fixed version: On Debian/Ubuntu: sudo apt install libsixel-dev or sudo apt install libsixel1; On Red Hat/CentOS: sudo yum install libsixel-devel
- 5. Verify the installed version is 1.8.7-r2 or later: dpkg -l | grep libsixel or rpm -qa | grep libsixel
- 6. Rebuild any applications that link against libsixel to ensure they use the updated library
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation2.0 h
- Testing2.0 h
- Review / QA1.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2026-44636 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-44636 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
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- Version or environment caveats, and links to real fixes
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