# imgproxy out-of-bounds heap read/write in ICO loader BMP header

Source: https://junglewise.ai/threats/go-2026-6895-imgproxy-has-out-of-bounds-heap-read-write-in-ico-loader-d8e85817  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-05. Updated: 2026-11-07  
License: CC BY 4.0 with a link back

Severity: info · Published 2026-11-05

imgproxy is an image processing service that converts and resizes images on demand. A flaw in its ICO (Windows icon) image loader allows attackers to crash worker processes by sending specially crafted image files, causing denial of service and preventing the service from handling legitimate image requests.

Technologies: [github.com/imgproxy/imgproxy (Go)](https://junglewise.ai/threats/technologies/github-com-imgproxy-imgproxy), [github.com/imgproxy/imgproxy/v2 (Go)](https://junglewise.ai/threats/technologies/github-com-imgproxy-imgproxy-v2), [github.com/imgproxy/imgproxy/v3 (Go)](https://junglewise.ai/threats/technologies/github-com-imgproxy-imgproxy-v3), [github.com/imgproxy/imgproxy/v4 (Go)](https://junglewise.ai/threats/technologies/github-com-imgproxy-imgproxy-v4), [Imgproxy](https://junglewise.ai/threats/technologies/imgproxy). Vendors: [Go](https://junglewise.ai/threats/vendors/go), [Imgproxy](https://junglewise.ai/threats/vendors/imgproxy).

## Quick answers

**Is This vulnerability exploited in the wild?** No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

**How severe is This vulnerability?** Informational severity, published 5 November 2026.

**Which products and versions are affected?** github.com/imgproxy/imgproxy (Go) SEMVER:introduced=0; github.com/imgproxy/imgproxy/v2 (Go) SEMVER:introduced=0; github.com/imgproxy/imgproxy/v3 (Go) SEMVER:introduced=3.3.0; github.com/imgproxy/imgproxy/v4 (Go) SEMVER:introduced=0,fixed=4.0.17; and 1 more.

**Is there a fix for This vulnerability?** Yes. github.com/imgproxy/imgproxy/v4 (Go): upgrade to 4.0.17 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is This vulnerability attacked?** It is attacked over the network.

**Am I affected?** Check whether you run github.com/imgproxy/imgproxy (Go), github.com/imgproxy/imgproxy/v2 (Go), github.com/imgproxy/imgproxy/v3 (Go) or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- github.com/imgproxy/imgproxy/v4 (Go): upgrade to 4.0.17 or later

  ```sh
  go get github.com/imgproxy/imgproxy/v4@v4.0.17
  ```


## Technical details

The ICO loader in imgproxy (vips/icoload.c) performs out-of-bounds heap read and write when reconstructing a BMP header from an ICO entry with insufficient image data. Unvalidated field reads from offsets +8, +14, and +32 in a tiny buffer, combined with heap writes at offset +22–+25, corrupt the size field of the following heap chunk, causing glibc's munmap_chunk() to abort deterministically. An unauthenticated remote attacker can trigger worker crash via a single crafted ICO request (network vector, no privileges required).

## Affected products

- imgproxy imgproxy 3.3.0 through 4.0.16

## Identifiers

- GHSA-494m-4556-wf5p
- GO-2026-6895

## Timeline

- 2026-10-06: disclosed
- 2026-10-06: patched: v4.0.17 released

## References

- [https://github.com/imgproxy/imgproxy/security/advisories/GHSA-494m-4556-wf5p](https://github.com/imgproxy/imgproxy/security/advisories/GHSA-494m-4556-wf5p)
- [https://github.com/imgproxy/imgproxy/commit/39fd9e844a8a46084161502e993d5a3c16ccf28d](https://github.com/imgproxy/imgproxy/commit/39fd9e844a8a46084161502e993d5a3c16ccf28d)

## Related threats

- [imgproxy integer overflow in ICO loader](https://junglewise.ai/threats/cve-2026-123614-imgproxy-from-4-0-0-before-4-0-16-contains-an-integer-overflow)
- [imgproxy unbounded memory allocation in ICO loader](https://junglewise.ai/threats/go-2026-6898-imgproxy-has-unbounded-memory-allocation-in-ico-loader-a99ea6ff)
- [imgproxy integer overflow in ICO loader](https://junglewise.ai/threats/go-2026-6897-imgproxy-has-integer-overflow-in-imgproxy-ico-loader-that-dbf52154)
- [imgproxy integer overflow in ICO loader](https://junglewise.ai/threats/imgproxy-has-integer-overflow-in-imgproxy-ico-loader-that-causes-denial-19f131eb)
- [imgproxy out-of-bounds write in ICO loader BMP header](https://junglewise.ai/threats/imgproxy-has-out-of-bounds-heap-read-write-in-ico-loader-bmp-header-c4e077cd)