HOMEVULNERABILITIESCVE-2021-23957
UNKNOWNCISA KEVIN THE WILD

CVE-2021-23957

Published: April 11, 2026

EPSS:0.28%probability of exploitation in 30 daysPercentile:51.8th

Official Description

Navigations through the Android-specific `intent` URL scheme could have been misused to escape iframe sandbox. Note: This issue only affected Firefox for Android. Other operating systems are unaffected. This vulnerability affects Firefox < 85.

NVD Source

Technical Analysis

CVE-2021-23957 requires local access, meaning attackers must already have a foothold on the target system.

Exploitation requires some privileges, which limits the exposure to scenarios where an attacker has already gained initial access.

CISA has added CVE-2021-23957 to the Known Exploited Vulnerabilities (KEV) catalog, confirming active exploitation in the wild. U.S. federal agencies are required to patch this within the mandated timeframe, and all organizations should treat remediation as urgent.

Exploit & PoC Resources

ACTIVE EXPLOITATIONConfirmed exploitation in the wild
Exploit-DB
Offensive Security exploit database
GitHub PoC Search
Community PoC repositories
Rapid7 / Metasploit
Metasploit module search
PacketStorm
Security advisories & exploits
NVD Detail
Official NIST entry
MITRE CVE
CVE Program entry
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Quick Facts

CVE IDCVE-2021-23957
Severity—
CISA KEVYES — Active Exploitation
ExploitIN THE WILD
EPSS (30d)0.28%
PublishedApr 11, 2026

Recommended Actions

  • →Apply vendor patches immediately
  • →Monitor CVE-2021-23957 in threat intel feeds
  • →Review IDS/IPS signatures for exploitation attempts
  • !CISA KEV: Federal agencies must patch per BOD 22-01 timeline
  • !Active exploitation confirmed — treat as P1
Data sourced from NVD (NIST), CISA KEV, and EPSS (FIRST). Analysis generated by CTIWATCH.COM. CVE data is provided under the NVD usage policy.
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