CVE-2021-30858
Apple iOS, iPadOS, macOS Use-After-Free Vulnerability
Description
CVE-2021-30858 is a HIGH vulnerability affecting Apple iOS, iPadOS, and macOS, carrying a CVSS 3.1 score of 8.8. Apple iOS, iPadOS, and macOS WebKit contain a use-after-free vulnerability that leads to code execution when processing maliciously crafted web content. Affected products include Apple iPadOS (>= 13.1, < 14.8), Apple iPhone OS (< 12.5.5; >= 13.0, < 14.8), Apple macOS (< 11.6). 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 0.00794 (73.76th percentile), this vulnerability demonstrates significant real-world exploitation activity and should be prioritized for immediate remediation.
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 | ipados | >= 13.1, < 14.8 |
| apple | iphone os | < 12.5.5; >= 13.0, < 14.8 |
| apple | macos | < 11.6 |
| fedoraproject | fedora | 33; 34 |
| debian | debian linux | 10.0; 11.0 |
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
- http://seclists.org/fulldisclosure/2021/Sep/25(Mailing List, Third Party Advisory)
- http://seclists.org/fulldisclosure/2021/Sep/27(Mailing List, Third Party Advisory)
- http://seclists.org/fulldisclosure/2021/Sep/29(Mailing List, Third Party Advisory)
- http://seclists.org/fulldisclosure/2021/Sep/38(Mailing List, Third Party Advisory)
- http://seclists.org/fulldisclosure/2021/Sep/39(Mailing List, Third Party Advisory)
- http://seclists.org/fulldisclosure/2021/Sep/50(Mailing List, Third Party Advisory)
- http://www.openwall.com/lists/oss-security/2021/09/20/1(Mailing List)
- http://www.openwall.com/lists/oss-security/2021/10/26/9(Mailing List)
- http://www.openwall.com/lists/oss-security/2021/10/27/1(Mailing List)
- http://www.openwall.com/lists/oss-security/2021/10/27/2(Mailing List)
- http://www.openwall.com/lists/oss-security/2021/10/27/4(Mailing List)
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/BO6DMTHZR57JDBOXPSNR2MKDMCRWV265/(Release Notes)
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/XYNV7ASK4LQVAUMJXNXBS3Z7RVDQ2N3W/(Release Notes)
- https://support.apple.com/en-us/HT212804(Third Party Advisory)
- https://support.apple.com/en-us/HT212807(Third Party Advisory)
- https://support.apple.com/kb/HT212824(Third Party Advisory)
- https://www.debian.org/security/2021/dsa-4975(Mailing List, Third Party Advisory)
- https://www.debian.org/security/2021/dsa-4976(Mailing List, Third Party Advisory)
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-30858(US Government Resource)
Weakness Type
CWE-416: Use After Free
CVE-2021-30858 is classified under CWE-416 — Use After Free. Use After Free (UAF) is a vulnerability that occurs when software continues to use a pointer after the memory it references has been freed. Once memory is freed, it may be reallocated for other purposes. If the dangling pointer is subsequently dereferenced, the program may read or write to memory now used for different data structures, leading to data corruption, information disclosure, or code execution. Use-after-free vulnerabilities are particularly prevalent in complex applications with manual memory management, including browsers, document parsers, and operating system kernels.
In the context of Apple WebKit, this weakness is particularly concerning because WebKit's complex memory management during web content processing creates numerous opportunities for use-after-free conditions. Attackers craft malicious web content that triggers specific memory allocation and deallocation sequences, then leverage the dangling pointer to achieve arbitrary code execution. Browser-based UAF vulnerabilities are highly valued by threat actors because they can be triggered simply by visiting a malicious web page, requiring minimal user interaction.
Learn more: CWE-416 — Use After Free
Impact Analysis
CVE-2021-30858 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, iPadOS, and macOS, including configuration files, credentials, and potentially data from connected systems.
Integrity (HIGH): Attackers can modify critical system files, install backdoors, alter configurations, or deploy malware on affected systems running Apple iOS, iPadOS, and macOS.
Availability (HIGH): Complete disruption of the affected service or system is possible, including denial of service, system crashes, or rendering the product 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, iPadOS, and macOS environment itself.
With an EPSS score of 0.00794 (73.76th percentile), this vulnerability ranks among the most likely to be exploited in real-world attacks, underscoring the urgency of remediation.
Exploit Maturity
CVE-2021-30858 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 0.00794 (73.76th percentile) places it among the most exploited vulnerabilities tracked.
Ransomware association: As of the latest KEV data, no direct ransomware association has been confirmed for CVE-2021-30858. However, the confirmed exploitation in the wild means threat actors are actively using this vulnerability in attacks.
Attack surface: The vulnerability's high EPSS score and KEV listing confirm that threat actors have developed and used working exploits. Public proof-of-concept code and exploitation tools are available, making this vulnerability accessible to a wide range of attackers. Organizations should assume that automated scanning and exploitation tools targeting this vulnerability are in active use.
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. Upgrade Apple iOS, iPadOS, and macOS to the latest patched version that addresses this vulnerability. Consult the official vendor advisory for specific patch guidance and release notes.
- Verify affected product versions in your environment. Identify all instances of Apple iOS, iPadOS, and macOS in your infrastructure (affected versions: Apple iPadOS (>= 13.1, < 14.8), Apple iPhone OS (< 12.5.5; >= 13.0, < 14.8), Apple macOS (< 11.6)). 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 network-level controls such as restricting access to the affected component, enabling enhanced logging, and monitoring for indicators of compromise.
- 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-2021-30858.
- 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-2021-30858 is a HIGH-severity vulnerability in Apple iOS, iPadOS, and macOS 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 use after free issue in WebKit allows arbitrary code execution when processing maliciously crafted web content. Fixed in iOS 14.8 and macOS Big Sur 11.6. The underlying flaw relates to use after free, which allows attackers to manipulate the application's processing logic in unintended ways. Successful exploitation enables arbitrary code execution on the target system, potentially leading to full system compromise.
CVSS 3.1 vector analysis: The vector 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. The Unchanged scope means impact is contained within the vulnerable component itself.
Frequently Asked Questions
Is CVE-2021-30858 being actively exploited?
Yes. CVE-2021-30858 is listed in CISA's Known Exploited Vulnerabilities (KEV) catalog, confirming active exploitation in the wild. With an EPSS score of 0.00794 (73.76th percentile), it ranks among the most exploited vulnerabilities tracked globally. Organizations should treat this as an immediate remediation priority.
What products are affected by CVE-2021-30858?
The affected products include Apple iPadOS (>= 13.1, < 14.8), Apple iPhone OS (< 12.5.5; >= 13.0, < 14.8), Apple macOS (< 11.6). 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-2021-30858?
Apply updates per vendor instructions. Ensure all affected instances of Apple iOS, iPadOS, and macOS are identified using vulnerability scanning and asset management tools. If immediate patching is not possible, implement network-level mitigations and enhanced monitoring. After patching, verify the fix and scan for indicators of prior compromise.
How severe is CVE-2021-30858?
CVE-2021-30858 is rated HIGH with a CVSS 3.1 score of 8.8. Its EPSS score of 0.00794 places it in the 73.76th 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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