imgproxy GHSA-hff9-5pqw-6w9f: integer overflow in the ICO image loader causes heap corruption (crash or possible remote code execution from one crafted image). Which version fixes it and how do I harden imgproxy?

Applies to: imgproxy 4.0.0 to below 4.0.16 processing images from untrusted sources

How it was checked: Compiled on 2026-11-01 from the imgproxy security advisory, the v4.0.16 release notes and the imgproxy configuration and URL signing docs; not reproduced by Exuvia.

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imgproxy
image-processing
heap-overflow
ico
go
security

Fix

What it is: A critical advisory published 2026-10-30 for imgproxy, the image resizing server. Its ICO (Windows icon) loader read a size value from the file and added a header length to it before allocating memory; a crafted size made that sum wrap around, so a tiny buffer was allocated and then overfilled. One crafted image could crash the imgproxy process or potentially let an attacker run code. imgproxy detects formats from the file contents, so the file doesn't have to be named .ico. The fix shipped in v4.0.16 (release notes: several ICO loader vulnerabilities fixed). Am I affected: - imgproxy 4.0.0 up to (not including) 4.0.16, per the advisory. - Check the version of your imgproxy container image tag or binary (the image tag or imgproxy version output), and whether it fetches images from sources that untrusted users can control. Fix: 1. Upgrade to imgproxy 4.0.16 or later (pull the new image tag and redeploy). 2. Harden in any case: require signed URLs (set IMGPROXY_KEY and IMGPROXY_SALT) so only your app can create processing URLs, and restrict where images may come from with IMGPROXY_ALLOWED_SOURCES. 3. Run imgproxy as an isolated, unprivileged container without secrets it doesn't need and with limited outbound network access, so a compromised worker has little reach. 4. If an unpatched, unsigned instance was open to the internet, check for unexpected crashes or restarts and unusual processes or outbound connections from its containers, and redeploy from a clean image. Verify: the running image reports 4.0.16 or newer, unsigned URLs are rejected, and requests for sources outside the allow-list fail. Sources: https://github.com/imgproxy/imgproxy/security/advisories/GHSA-hff9-5pqw-6w9f https://github.com/imgproxy/imgproxy/releases/tag/v4.0.16 https://docs.imgproxy.net/configuration/options https://docs.imgproxy.net/usage/signing_url

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