# CVE-2026-40492: SAIL has heap buffer overflow in XWD decoder — bits_per_pixel vs pixmap_depth type confusion in byte-swap

> A heap buffer overflow in the SAIL image library's XWD decoder allows attackers to execute arbitrary code or cause denial of service via crafted images.

- **Severity:** Critical 9.8 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 18 Apr 2026
- **Updated:** 20 Apr 2026
- **Also known as:** DEBIAN-CVE-2026-40492, GHSA-526v-vm72-4v64, UBUNTU-CVE-2026-40492

## What is CVE-2026-40492?

CVE-2026-40492 is a critical memory corruption vulnerability in HappySeaFox sail, published on 18 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

SAIL is a cross-platform library for loading and saving images with support for animation, metadata, and ICC profiles. Prior to commit 36aa5c7ec8a2bb35f6fb867a1177a6f141156b02, the XWD codec resolves pixel format based on `pixmap_depth` but the byte-swap code uses `bits_per_pixel` independently. When `pixmap_depth=8` (BPP8_INDEXED, 1 byte/pixel buffer) but `bits_per_pixel=32`, the byte-swap loop accesses memory as `uint32_t*`, reading/writing 4x the allocated buffer size. This is a different vulnerability from the previously reported GHSA-3g38-x2pj-mv55 (CVE-2026-27168), which addressed `bytes_per_line` validation. Commit 36aa5c7ec8a2bb35f6fb867a1177a6f141156b02 contains a patch.

Weakness: CWE-787 (Out-of-bounds Write)

## Which versions are affected by CVE-2026-40492?


## How do I fix CVE-2026-40492?

Apply the vendor's patch.

## Is CVE-2026-40492 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40492 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-40492 and fix it if it is affected.

What it is: CVE-2026-40492 is a critical memory corruption vulnerability in HappySeaFox sail, published on 18 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-40492 exists.

Affected product: HappySeaFox sail. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-40492/ (Markdown: https://insights.sbomify.com/CVE-2026-40492/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-40492
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-40492
- OSV: https://osv.dev/vulnerability/CVE-2026-40492

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-40492/
Summaries are generated and may contain mistakes; the official description above is the record.