Memory corruption via split Promise callback state
Published May 17, 2025 · Updated Apr 13, 2026
Out-of-bounds access in affected Mozilla Firefox and Thunderbird releases allows remote attackers to read or write process memory. The Promise.allSettled implementation tracked paired fulfillment and rejection callbacks separately, exposing its result array to JavaScript before the alternate callback could access it again. Execution of attacker-controlled JavaScript is required; successful exploitation can disclose process data, corrupt memory, or destabilize the application.
Summary
What happened
Out-of-bounds access in affected Mozilla Firefox and Thunderbird releases allows remote attackers to read or write process memory. The Promise.allSettled implementation tracked paired fulfillment and rejection callbacks separately, exposing its result array to JavaScript before the alternate callback could access it again. Execution of attacker-controlled JavaScript is required; successful exploitation can disclose process data, corrupt memory, or destabilize the application.
The record
- CVE
- CVE-2025-4918
- Published
- May 17, 2025
- Updated
- Apr 13, 2026
- Vendor
- Unknown vendor
- Product
- Unknown product
- Classifications
- CWE-125, CWE-787, T1203
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- May 16, 2025Exploitation reportedPwn2Own 2025 demonstration
- May 17, 2025CVE publishedPublication date reported by the CVE source.
- Apr 13, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
What conditions does exploitation require?
What is affected?
Affected products and versions are unavailable in this record.
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- Mozilla Bugzilla Promise.allSettled proof of conceptproof of concept · demonstrated
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Reported exploitation
- Pwn2Own 2025 demonstrationreported exploitation
Technologies
Your stack
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Your stack
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