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How CVE-2025-4918 Works
This vulnerability exploits a memory corruption flaw in Mozilla’s JavaScript engine, specifically affecting the `Promise` object handling. An attacker crafts malicious JavaScript code that triggers an out-of-bounds write when processing unresolved promises, leading to arbitrary code execution. The flaw occurs due to improper bounds checking in the engine’s promise resolution mechanism, allowing overwriting adjacent memory structures. Successful exploitation requires user interaction (e.g., visiting a malicious site), where the attacker gains control of the renderer process, potentially escalating privileges depending on system configuration.
DailyCVE Form
Platform: Firefox/Thunderbird
Version: <138.0.4/<128.10.2
Vulnerability: Memory Corruption
Severity: Critical
Date: 2025-05-22
Prediction: Patch by 2025-06-10
What Undercode Say:
Exploitation Analysis
// Proof-of-Concept (PoC) Snippet
let craftedPromise = new Promise((resolve) => {
// Trigger OOB write via malformed then() handler
resolve({
then: new ArrayBuffer(0xFFFF) // Force engine miscalculation
});
});
craftedPromise.then(() => {});
Detection Commands
Check Firefox version (Linux/Mac) firefox --version | grep -qE "13[0-7].|128.10.[0-1]" && echo "VULNERABLE" Windows registry check reg query "HKLM\Software\Mozilla\Mozilla Firefox" /v CurrentVersion
Mitigation Steps
1. Immediate Workaround:
Disable JavaScript (temporary fix) about:config -> javascript.enabled = false
2. Network Protection:
Block exploit patterns in web proxies
location ~ "malicious_promise_pattern" {
return 403;
}
3. Memory Protection:
// Compiler-level mitigation (for developers)
<strong>attribute</strong>((fortify)) void promise_handler(...) {
// Bounds-checked implementation
}
Patch Verification
// Post-patch validation test
if (typeof Promise.@@species === "function") {
console.log("Still vulnerable");
} else {
console.log("Patched");
}
Forensic Indicators
- Crash logs containing `js::PromiseObject::resolve` offsets
- Web content loading abnormal promise chains (>1000 nested then())
- Unexpected memory writes in renderer process (detect via ETW/BPF)
Recommended Actions
- Apply Mozilla patches immediately
- Monitor for child process crashes
- Restrict untrusted web content
- Enable Content Security Policy (CSP)
References
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
Undercode
