CVE-2021-30761
Apple iOS WebKit Memory Corruption Vulnerability
Description
CVE-2021-30761 is a HIGH iOS WebKit Memory Corruption Vulnerability affecting Apple iOS, carrying a CVSS 3.1 score of 8.8. A memory corruption issue was addressed with improved state management. This issue is fixed in iOS 12.5.4. Processing maliciously crafted web content may lead to arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited.. Affected products include Iphone Os (< 12.5.4). This CVE is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog with a remediation deadline of 2021-11-17. With an EPSS score of 0.0037 (58.48th percentile), this vulnerability shows moderate exploitation probability and warrants prompt attention.
KEV Information
CVSS Score
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:HOpen in CalculatorAffected Products
| Vendor | Product | Version |
|---|---|---|
| apple | iphone os | < 12.5.4 |
Multiple CVSS Assessments
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
References
- https://support.apple.com/en-us/HT212548(Release Notes, Vendor Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-30761(Third Party Advisory, US Government Resource)
Weakness Type
CWE-787: Out-of-bounds Write
CVE-2021-30761 is classified under CWE-787 — Out-of-bounds Write. Out-of-bounds Write occurs when a product writes data past the end, or before the beginning, of the intended buffer. This can result in corruption of data, a crash, or arbitrary code execution. Memory corruption through out-of-bounds writes is one of the most dangerous vulnerability classes, frequently enabling remote code execution.
In the context of Apple iOS, this weakness is particularly concerning because out-of-bounds write vulnerabilities in rendering engines and media processing components can be triggered remotely through specially crafted content. When processing malicious input, the write operation corrupts adjacent memory structures, which attackers leverage to redirect control flow and execute arbitrary code. This class of vulnerability has been extensively exploited in web browsers and multimedia frameworks to achieve full system compromise from a single interaction.
Learn more: CWE-787 — Out-of-bounds Write
Impact Analysis
CVE-2021-30761 carries a CVSS 3.1 score of 8.8 (HIGH) with Unchanged Scope.
Confidentiality (HIGH): Successful exploitation grants the attacker extensive access to sensitive data processed by Apple iOS, including protected system information, user data, and potentially credentials or tokens stored within the affected environment.
Integrity (HIGH): Attackers can modify critical system files, bypass security controls, alter configurations, or deploy malicious payloads on affected Apple iOS systems.
Availability (HIGH): Complete disruption of the affected service or system is possible, including denial of service, system crashes, or rendering Apple iOS inoperable.
Scope Unchanged: The vulnerability's scope is Unchanged (U), meaning exploitation is contained within the vulnerable component. The impact, while significant, is limited to the Apple iOS environment itself.
With an EPSS score of 0.0037 (58.48th percentile), this vulnerability demonstrates notable exploitation probability and warrants prompt remediation.
Exploit Maturity
CVE-2021-30761 has confirmed active exploitation in the wild and is listed in CISA's Known Exploited Vulnerabilities catalog.
Exploit status: This vulnerability has been actively exploited, as confirmed by its inclusion in the KEV catalog. The EPSS score of 0.0037 (58.48th percentile) confirms significant exploitation activity.
Ransomware association: As of the latest KEV data, no direct ransomware association has been confirmed for CVE-2021-30761. However, the confirmed exploitation in the wild means threat actors are actively using this vulnerability in attacks.
Attack surface: The network-based attack vector significantly broadens the attack surface, as any system with network exposure running affected versions is potentially vulnerable. Remote exploitation without physical access makes this particularly dangerous for internet-facing deployments.
KEV deadline: CISA required federal agencies to remediate this vulnerability by 2021-11-17. All organizations should treat this deadline as a strong recommendation for their own remediation timelines.
Remediation
- Apply vendor patches immediately. Apply updates per vendor instructions. Consult the vendor advisory for specific patch guidance and verify the patch addresses CVE-2021-30761 in your specific product version.
- Verify affected product versions in your environment. Identify all instances of Apple iOS in your infrastructure (affected versions: Iphone Os (< 12.5.4)). Use asset inventory and vulnerability scanning tools to ensure no instances are missed.
- Implement interim mitigations if patching is delayed. If immediate patching is not feasible, apply compensating controls such as restricting access to the affected component, enabling enhanced logging and monitoring, and enforcing least-privilege principles for running applications.
- Scan for signs of prior exploitation. Given the confirmed active exploitation of this vulnerability, review system logs and security monitoring data for evidence of compromise. Conduct a thorough investigation if any suspicious activity is detected.
- Update detection signatures and monitoring rules. Ensure intrusion detection and prevention systems, endpoint detection tools, and SIEM rules are updated to detect exploitation attempts targeting CVE-2021-30761.
- Conduct a post-remediation review. After patching, verify the fix is effective and document the remediation actions taken. Update your vulnerability management records and assess whether any additional hardening measures are warranted.
Technical Details
CVE-2021-30761 is a HIGH-severity vulnerability in Apple iOS that can be exploited remotely over the network without physical access. The attack complexity is low, meaning no specialized conditions or preparation are required beyond the attack prerequisites. No prior authentication or privileges are needed to initiate the attack. User interaction is required, meaning a victim must perform an action such as opening a file, clicking a link, or visiting a website for exploitation to succeed.
Technical mechanism: A memory corruption issue was addressed with improved state management. This issue is fixed in iOS 12.5.4. Processing maliciously crafted web content may lead to arbitrary code execution. Apple is aware of a report that this issue may have been actively exploited.. The underlying flaw relates to out-of-bounds write, where out-of-bounds Write occurs when a product writes data past the end, or before the beginning, of the intended buffer. This can result in corruption of data, a crash, or arbitrary code execution. Memory corruption through out-of-bounds writes is one of the most dangerous vulnerability classes, frequently enabling remote code execution.
Affected products: Apple Iphone Os (< 12.5.4)
CVSS 3.1 vector analysis: The vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H reflects an Attack Vector of NETWORK, Attack Complexity of LOW, Privileges Required of NONE, User Interaction of REQUIRED, Scope UNCHANGED, and impact ratings of HIGH/HIGH/HIGH for Confidentiality/Integrity/Availability respectively.
Frequently Asked Questions
What is CVE-2021-30761?
CVE-2021-30761 is a HIGH-severity vulnerability (CVSS 8.8) in Apple iOS. Apple iOS WebKit contains a memory corruption vulnerability that leads to code execution when processing maliciously crafted web content. This vulnerability could impact HTML parsers that use WebKit, including but not limited to Apple Safari and non-Apple products which rely on WebKit for HTML processing. It is listed in CISA's Known Exploited Vulnerabilities catalog, confirming real-world exploitation.
Which products are affected by CVE-2021-30761?
The affected products include Iphone Os (< 12.5.4). Organizations running any of these versions should verify their exposure and prioritize remediation. Check vendor advisories for the complete and most current list of affected versions.
How do I fix CVE-2021-30761?
Apply updates per vendor instructions. Ensure all affected instances of Apple iOS are identified using vulnerability scanning and asset management tools. If immediate patching is not possible, implement compensating controls and enhanced monitoring. After patching, verify the fix and scan for indicators of prior compromise.
How severe is CVE-2021-30761?
CVE-2021-30761 is rated HIGH with a CVSS 3.1 score of 8.8. Its EPSS score of 0.0037 places it in the 58.48th percentile for exploitation likelihood. The vulnerability has confirmed active exploitation in the wild and was required to be remediated by federal agencies by 2021-11-17 per CISA's KEV directive.
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