CVE-2026-8257 WebAssembly Binaryen BrOn wasm-ir-builder.cpp makeBrOn assertion
A local attacker can trigger a reachable assertion in the BrOn parser, causing a denial of service in WebAssembly Binaryen.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-8257?
CVE-2026-8257 is a medium-severity denial of service vulnerability in WebAssembly Binaryen, published on 11 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
A vulnerability was detected in WebAssembly Binaryen up to 117. This issue affects the function IRBuilder::makeBrOn of the file src/wasm/wasm-ir-builder.cpp of the component BrOn Parser. Performing a manipulation results in reachable assertion. The attack needs to be approached locally. The exploit is now public and may be used. The patch is named 1251efbc1ea471c1311d2726b2bbe061ff2a291c. It is suggested to install a patch to address this issue.
Weakness: CWE-617
Which versions are affected by CVE-2026-8257?
It affects 1 product.
Products include Webassembly Binaryen.
How do I fix CVE-2026-8257?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-8257 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-8257 exists.
Other vulnerabilities in WebAssembly Binaryen
Sources
Also known as DEBIAN-CVE-2026-8257, GHSA-gmmj-chcc-2f2x, JLSEC-2026-1094, UBUNTU-CVE-2026-8257.