CVE-2026-112398: Pillow: Heap buffer overflow in FlashPix (FPX) JPEG decoding leads to code execution

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.3%, percentile 24: FIRST’s model estimates a 0.3% chance of exploitation activity in the next 30 days, higher than 24% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes pillow (PyPI) <= 12.3.0, fixed in 13.0.0. Check your lockfile, including transitive dependencies.

What it is

Pillow is a Python imaging library. Prior to 13.0.0, Pillow's FlashPix JPEG-tile decoder can write decoded scanlines beyond the allocated tile buffer. FlashPix (FPX) JPEG decoding selects raw mode LA with two bytes per pixel, while an unrecognized JPEG mode can be decoded as JCSUNKNOWN with four components, causing ImagingJpegDecode to write four-component scanlines into the two-byte tile buffer. An attacker can supply a crafted OLE2 FlashPix file to an application with the optional olefile dependency installed that opens or thumbnails untrusted input. This can corrupt heap memory and may allow arbitrary code execution. This issue is fixed in version 13.0.0.

From the GitHub advisory

Credits

Researcher: Alex Bouffard (mixbo@pebwalker.com)

Summary

A heap buffer overflow in Pillow's FlashPix (FPX) JPEG-tile decoder lets an attacker achieve arbitrary code execution by getting an application to open a single crafted file with Image.open(). The file is recognized by content (the OLE2 magic), not by extension, so any service that opens or thumbnails untrusted uploads with the optional olefile dependency installed is reachable with no user interaction. In the PoC below, opening one crafted file executes an attacker-chosen command on stock Pillow 12.2.0 (x8664 Ubuntu 24.04, glibc 2.39).

Details

Weakness type: CWE-122, CWE-787.

Product: pillow (PyPI) · Assigned by: GitHub_M · Published: 2026-10-19

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: high (needs special conditions)
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-23): 0.32% probability of exploitation activity in the next 30 days; percentile 24.

Timeline

• 2026-10-19 — CVE record published by GitHub_M
• 2026-10-22 — CVE record last updated
• 2026-10-23 — GitHub-reviewed advisory GHSA-5x8w-8jj5-q52h published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-5x8w-8jj5-q52h github.com
2. CVE.org record CVE-2026-112398 cve.org
3. NVD entry CVE-2026-112398 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com

Critical PyPI advisories · Today’s Security Digest