Medium exploit reference

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

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.

Published May 10, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: VulDB

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.2% (30-day exploitation probability)+1
Technical severity (medium)+3
CISA SSVC: exploitation "poc"+5

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.19%

ahead of 8% of scored CVEs · Oct 15, 2026

Affects

Webassembly

Binaryen

CVSS base

5.5

Medium · 3 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

Proof of concept

none · proof-of-concept · active

Automatable

can an attacker script the kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

Documented patch — github.com (NIST National Vulnerability Database)
Documented patch — github.com (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Webassembly Binaryen).
Apply the fixed version or the patch documented under Remediation.
Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Webassembly	Binaryen	≤ 117	Vulnerable	NIST National Vulnerability Database
Webassembly	Binaryen	version 117	Vulnerable	CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Local

Attack complexity

Low

Privileges required

Low

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
4.8	CVSS 4.0	Medium	—	—	VulDB via CVE Program (cve.org) e CISA ADP
1.9	CVSS 4.0	Low	—	—	cna@vuldb.com via NIST National Vulnerability Database
5.5	CVSS 3.1	Medium	1.8	3.6	nvd@nist.gov via NIST National Vulnerability Database
3.3	CVSS 3.1	Low	1.8	1.4	cna@vuldb.com via NIST National Vulnerability Database
3.3	CVSS 3.1	Low	—	—	VulDB via CVE Program (cve.org) e CISA ADP
3.3	CVSS 3.0	Low	—	—	VulDB via CVE Program (cve.org) e CISA ADP
1.7	CVSS 2.0	Low	3.1	2.9	cna@vuldb.com via NIST National Vulnerability Database
1.7	CVSS 2.0	Low	—	—	VulDB via CVE Program (cve.org) e CISA ADP

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov)

Scoring entities (NIST, CNA, ADP) score independently; each score is shown with its origin. For prioritization we use 5.5 (NVD (NIST)) as a conservative provisional reference — not a definitive official score.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-617

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 15, 2026 · 3 reading(s) · max 0.19%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.

endpoint telemetry (EDR)

Timeline

What happened to this CVE, newest first.

2026
Affected products added · webassembly/binaryen
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 13, 2026
Fix documented
Oct 13, 2026 · NIST National Vulnerability Database
CVSS changed · 5.5
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Analyzed
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
May 10, 2026 · VulDB

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

8 on the record

github.com/WebAssembly/binaryen/pull/8635
Mitigation, Patch, issue-tracking, patch, NIST National Vulnerability Database
github.com/WebAssembly/binaryen/commit/1251efbc1ea471c1311d2726b2bbe061ff2a291c
Patch, patch, NIST National Vulnerability Database
github.com/HackC0der/CVE-Repos/blob/main/wasm-binaryen/Assertion_Failure_isRef_w
Exploit, exploit, patch, NIST National Vulnerability Database
vuldb.com/submit/809552
Third Party Advisory, VDB Entry, third-party-advisory, NIST National Vulnerability Database
vuldb.com/vuln/362554
Third Party Advisory, VDB Entry, vdb-entry, technical-description, NIST National Vulnerability Database
vuldb.com/vuln/362554/cti
Permissions Required, VDB Entry, signature, permissions-required, NIST National Vulnerability Database
github.com/WebAssembly/binaryen/
Product, product, NIST National Vulnerability Database
github.com/WebAssembly/binaryen/issues/8633
Exploit, Issue Tracking, Third Party Advisory, issue-tracking, NIST National Vulnerability Database

Elsewhere on this site

Webassembly
every CVE for this vendor

CWE-617
other pages naming this weakness

Related CVEs (same products)

High CVE-2025-14956 WebAssembly Binaryen wasm-binary.cpp readExport heap-based overflow Dec 19, 2025
Medium CVE-2025-14957 WebAssembly Binaryen IRBuilder wasm-ir-builder.cpp makeLocalTee null pointer dereference Dec 19, 2025

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-8257 is "WebAssembly Binaryen BrOn wasm-ir-builder.cpp makeBrOn assertion", rated Medium. It affects Binaryen (Webassembly); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.5 describes technical severity. EPSS 0.19% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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