GHSA-5xmw-vc9v-4wf2 BIT-pillow-2026-42309 CVE-2026-42309 PYSEC-2026-2251

Pillow has a heap buffer overflow with nested list coordinates

Medium PyPI

Severity: 0.0 / 10; Medium · CVSS 4.0
Exploit chance (EPSS): 0.13%; Chance of exploitation in the next 30 days. Higher than 2.79% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-122 Heap-based Buffer Overflow
Fix: 12.2.0; Upgrade pillow to this version or later

Description

Passing nested lists as coordinates to APIs that accept coordinates such as ImagePath.Path, ImageDraw.ImageDraw.polygon and ImageDraw.ImageDraw.line could cause a heap buffer overflow, as nested lists were recursively unpacked beyond the allocated buffer. Coordinate lists are now validated to contain exactly two numeric coordinates. This was introduced in Pillow 11.2.1.

Affected versions

PyPI

Package	Vulnerable	Fixed in
pillow	`>= 11.2.1, < 12.2.0`	`12.2.0`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

pillow PyPI → `12.2.0`

pip

pip install --upgrade "pillow>=12.2.0"

poetry

poetry add "pillow>=12.2.0"

uv

uv add "pillow>=12.2.0"

Severity breakdown

CVSS 4.0 0.0

CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Attack vector: Local
Attack complexity: Low
Attack requirements: None
Privileges required: None
User interaction: None
Confidentiality (vulnerable system): None
Integrity (vulnerable system): None
Availability (vulnerable system): Low
Confidentiality (subsequent systems): None
Integrity (subsequent systems): None
Availability (subsequent systems): None

CVSS 3.1 5.5

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Attack vector: Local
Attack complexity: Low
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Weakness

CWE-122: Heap-based Buffer Overflow

A heap overflow condition is a buffer overflow, where the buffer that can be overwritten is allocated in the heap portion of memory, generally meaning that the buffer was allocated using a routine such as malloc().

How to prevent it

Pre-design: Use a language or compiler that performs automatic bounds checking.
Architecture and Design: Use an abstraction library to abstract away risky APIs. Not a complete solution.
Operation, Build and Compilation: Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.
Operation, Build and Compilation: Run or compile the software using features or extensions that randomly arrange the positions of a program's executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code. Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as "rebasing" (for Windows) and "prelinking" (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking. For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].
Implementation: Implement and perform bounds checking on input.
Implementation: Do not use dangerous functions such as gets. Look for their safe equivalent, which checks for the boundary.
Operation: Use OS-level preventative functionality. This is not a complete solution, but it provides some defense in depth.

References

Advisories

nvd.nist.gov/vuln/detail/CVE-2026-42309

Packages

github.com/python-pillow/Pillow

Timeline

May 4, 2026 Published
Oct 19, 2026 Last updated by the source
Nov 1, 2026 Latest EPSS score

Advisory	Severity	Why it's related
PYSEC-2023-175 Pillow versions before v10.0.1 bundled libwebp binaries in wheels that are vulnerable to CVE-2023-5129 (previously CVE-2023-4863).	High Known exploited	Also affects pillow
GHSA-j7hp-h8jx-5ppr libwebp: OOB write in BuildHuffmanTable	High Known exploited	Also affects pillow
GHSA-78g4-xqwv-q3g8 Pillow: Bundled libopenjp2 2.5.4 in all wheels since 11.1.0 carries OSV-2025-219 heap-buffer-overflow write reachable from Image.open().load()	High	Also affects pillow
GHSA-654x-cwwv-5j9c Pillow: Arrow export leaks stale heap memory when PILLOW_ALIGNMENT > 1	Medium	Also affects pillow
GHSA-xvh5-g6gv-559v Pillow: Memory disclosure and segfault in libtiff encoder via crafted TIFF tags	High	Also affects pillow
GHSA-g7cr-3p24-7wf7 Pillow: Heap buffer overflow writing JPEG comment after ICC profile fills buffer	High	Also affects pillow
GHSA-9v9v-9qvf-h2hj Pillow: Heap over-read in WMF/EMF rendering via 16-bit dimension truncation (Windows builds)	High	Also affects pillow
GHSA-g4qv-2jxx-769h Pillow: PNG eXIf chunk makes EXIF parsing run in quadratic time	Medium	Also affects pillow

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