The Aug 31 patch brings back the AVIF output that the critical Aug 25 security release disabled, but only when your installed sharp resolves to 0.35.4 or newer.
Next.js 16.3.4, out Aug 31, flips AVIF image optimization back on. The Aug 25 security release, 16.3.3, had disabled AVIF output to close a critical unauthenticated RCE in the Image Optimization API triggered by crafted AVIF files (GHSA-2xp9-vwfh-vxw4). Six days later, the capability is back.
The restore is not unconditional. Vercel re-enabled AVIF through a backport that now requires sharp ^0.35.4, the patched version of the dependency the exploit ran through. AVIF output only returns when your installed sharp clears that bar. The 15.5 LTS line gets the same treatment in 15.5.25.
If you use next/image with AVIF and pulled 16.3.3, you have been silently serving non-AVIF output since Aug 25. Update to 16.3.4 (or 15.5.25) with npm install next@16.3.4, then verify your lockfile resolves sharp to 0.35.4 or newer. If you pinned sharp below that to dodge the advisory, the re-enable will not help you until you move it.
16.3.4 also backports a testmode infinite-recursion fix, a build error when aliasing typescript to @typescript/typescript6, and unset crossOrigin in Turbopack manifests. Treat AVIF as the reason to ship this one today.
Next.js moved its August security release forward to Aug 25, shipping 16.3.3 and 15.5.24 to close two critical RCEs, a Windows-only path traversal and a crafted-AVIF image optimization exploit.
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sharp below 0.35.4 inherits two libheif flaws rated critical upstream that can reach remote code execution on glibc-based Linux. The fix is a version bump or a one-line AVIF block.
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