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CriticalVulnerabilityGHSA-hff9-5pqw-6w9fupdated 30 Oct 2026, 22:57 UTC

imgproxy image processing flaw in ICO loader can crash or take over server

Someone can send a specially crafted ICO image file to imgproxy and make the server crash or, in the worst case, let the attacker run their own code on it. No login is needed to send the image.

Fixed in 4.0.16 · out Official source
SeverityCriticalCVSS 9.8 of 10
Being exploited?UnclearNo reports either way yet
Fix available?Yes4.0.16 · since 30 Oct 2026
How sure is this?Official sourceBacked by an official source

How the attack works simplified

  1. 1Attacker sends ICOCrafted file with oversized size field
  2. 2imgproxy reads headerSize value wraps around in math
  3. 3Tiny buffer allocatedOnly 3 bytes reserved
  4. 4Heap overwrittenImage data written past buffer
  5. ResultServer crashes or attacker gains code execution

What happened

The ICO image loader in imgproxy computes a memory allocation size from an attacker-controlled 32-bit value; the addition wraps around, causing a too-small heap allocation that is then overwritten (heap buffer overflow).

Why it is dangerous: A remote, unauthenticated attacker can crash the imgproxy process (denial of service) or potentially achieve remote code execution through heap corruption, affecting any internet-facing imgproxy instance that processes ICO images.

Are you affected?

You are affected if you run imgproxy 4.0.0 up to but not including 4.0.16 (Go module github.com/imgproxy/imgproxy, v2 or v3 paths) and it can process ICO images.

Package / productAffected versionsFixed in
github.com/imgproxy/imgproxy/v3 · go>= 4.0.0, < 4.0.164.0.16
github.com/imgproxy/imgproxy/v2 · go>= 4.0.0, < 4.0.164.0.16
github.com/imgproxy/imgproxy · go>= 4.0.0, < 4.0.164.0.16

What to do

  1. Upgrade imgproxy to version 4.0.16 or later
  2. If you cannot upgrade right away, block or disable ICO input processing at your proxy or in imgproxy's configuration
  3. Check logs for crashes or unusual requests involving ICO files

Timeline

  1. 30 Oct 2026, 22:57 UTC
    Publicly disclosed
  2. 30 Oct 2026, 22:57 UTC
    Reported by GitHub Advisory · GitHub Advisory
  3. 30 Oct 2026, 22:57 UTC
    Picked up by Zero Radar

Sources 1 report, oldest first

Official vendor, government CERT or advisory database

Technical details

ID
GHSA-hff9-5pqw-6w9f
CVSS
9.8 / 10
Disclosed
30 Oct 2026, 22:57 UTC
On Zero Radar
30 Oct 2026, 22:57 UTC (0 min after disclosure)
Last change
30 Oct 2026, 22:57 UTC

The plain-language parts and the attack diagram were written by an AI model (anthropic/claude-haiku-5.5) from the sources above. Facts like versions, exploitation and dates come from the sources themselves. How Zero Radar works

imgproxy image processing flaw in ICO loader can crash or take over server · Zero Radar