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PatchSiren cyber security CVE debrief

CVE-2026-8257 WebAssembly CVE debrief

CVE-2026-8257 is a low-severity Binaryen flaw that can trigger a reachable assertion in the BrOn parser path. The issue is reported in Binaryen up to 117 and is tied to IRBuilder::makeBrOn in src/wasm/wasm-ir-builder.cpp. Source data indicates the attack is local, with a public exploit reference and a vendor patch available.

Vendor
WebAssembly
Product
Binaryen
CVSS
LOW 1.9
CISA KEV
Not listed in stored evidence
Original CVE published
2026-05-11
Original CVE updated
2026-05-21
Advisory published
2026-05-11
Advisory updated
2026-05-21

Who should care

Teams that build, test, or transform WebAssembly using WebAssembly Binaryen, especially if they run Binaryen locally on untrusted or attacker-influenced inputs. Security and release owners for downstream tooling should prioritize patching if Binaryen 117 or earlier is in use.

Technical summary

NVD data marks CVE-2026-8257 as affecting cpe:2.3:a:webassembly:binaryen versions through 117. The weakness is labeled CWE-617. The issue is described as a manipulation that causes a reachable assertion in IRBuilder::makeBrOn within src/wasm/wasm-ir-builder.cpp. The CVSS v4 vector indicates a local attack with low availability impact. References include a patch commit (1251efbc1ea471c1311d2726b2bbe061ff2a291c), a related pull request, and an issue tracker entry referencing exploit activity.

Defensive priority

Low overall severity, but patch promptly if Binaryen is used in build pipelines or other local processing of untrusted WebAssembly inputs. Reachable assertions can still disrupt tooling and automated workflows.

Recommended defensive actions

  • Update WebAssembly Binaryen to a version that includes commit 1251efbc1ea471c1311d2726b2bbe061ff2a291c.
  • If immediate upgrading is not possible, restrict who can feed inputs into Binaryen-based local tooling and review any untrusted WebAssembly ingestion paths.
  • Monitor downstream build and analysis systems for crashes or assertion failures involving IRBuilder::makeBrOn.
  • Track the linked issue and pull request for any follow-up fixes or backports.
  • Treat Binaryen 117 and earlier as vulnerable in your internal asset inventory until patched.

Evidence notes

Facts in this debrief are drawn from the provided NVD record and linked references. The CVE was published on 2026-05-11 and modified on 2026-05-21. NVD lists Binaryen versions up to 117 as vulnerable, with a local attack vector and CWE-617. The source references include the patch commit 1251efbc1ea471c1311d2726b2bbe061ff2a291c, a related issue, a related pull request, and a third-party exploit reference. No unsupported exploit details are included here.

Official resources

Published 2026-05-11T02:16:27.090Z; last modified 2026-05-21T17:59:57.330Z.