Apple iOS, iPadOS, macOS Use-After-Free
CVE-2021-30858 is a high-severity use after free vulnerability in macOS from Apple, with a CVSS 3.1 base score of 8.8 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, but only if a user takes part, for example by opening a link or file. The record lists version 11.6 as the first without the flaw, so updating macOS to that release or later removes the exposure. CISA added it to the Known Exploited Vulnerabilities catalogue on November 3, 2021, which means attacks have been observed in the wild.
Attackers are already exploiting this vulnerability, according to CISA.
What to do
- Update macOS to 11.6 or a later version.
- Update iOS to 14.8 or a later version.
- Update iPadOS to 14.8 or a later version.
- CISA's required action: Apply updates per vendor instructions.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
- Because the attack needs a user to take part, warn users about unexpected links and files related to this product until it is patched.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Apple | macOS | before 11.6 | 11.6 |
| Apple | iOS | before 14.8 | 14.8 |
| Apple | iPadOS | 13.1 up to, but not including, 14.8 | 14.8 |
| Apple | Iphone OS | before 12.5.5; 13.0 up to, but not including, 14.8 | 12.5.5, 14.8 |
| Fedora Project | Fedora | 33; 34 | Not stated |
| Debian | Debian Linux | 10.0; 11.0 | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- RequiredA user must take an action such as opening a file or link.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 8.8 | High | NVD |
| CVSS 3.1 | 8.8 | High | CISA (ADP) |
| CVSS 2.0 | 6.8 | Medium | NVD |
Official description
A use after free issue was addressed with improved memory management. This issue is fixed in iOS 14.8 and iPadOS 14.8, macOS Big Sur 11.6. 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Timeline
- CVE record published.
- Added to CISA's Known Exploited Vulnerabilities catalogue.
- Deadline for US federal agencies to remediate, set by CISA.
- CISA published its SSVC assessment (exploitation: active, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Third-party and government advisories
- seclists.org/fulldisclosure/2021/Sep/25Mailing List, Third Party Advisory
- seclists.org/fulldisclosure/2021/Sep/27Mailing List, Third Party Advisory
- seclists.org/fulldisclosure/2021/Sep/29Mailing List, Third Party Advisory
- seclists.org/fulldisclosure/2021/Sep/38Mailing List, Third Party Advisory
- seclists.org/fulldisclosure/2021/Sep/39Mailing List, Third Party Advisory
- seclists.org/fulldisclosure/2021/Sep/50Mailing List, Third Party Advisory
- support.apple.com/en-us/HT212804Third Party Advisory
- support.apple.com/en-us/HT212807Third Party Advisory
- support.apple.com/kb/HT212824Third Party Advisory
- debian.org/security/2021/dsa-4975Mailing List, Third Party Advisory
- debian.org/security/2021/dsa-4976Mailing List, Third Party Advisory
- cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-30858US Government Resource
Other references
- openwall.com/lists/oss-security/2021/09/20/1Mailing List
- openwall.com/lists/oss-security/2021/10/26/9Mailing List
- openwall.com/lists/oss-security/2021/10/27/1Mailing List
- openwall.com/lists/oss-security/2021/10/27/2Mailing List
- openwall.com/lists/oss-security/2021/10/27/4Mailing List
Other vulnerabilities in macOS
- 8.8 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
- 7.5 High severity
Recent Use After Free vulnerabilities
- 7.8 High severity
- 8.8 High severity
Google Chromium WebGL Use-After-Free Exploited
- 8.8 High severity
- 9.8 Critical severity
- 8.8 High severity
- 7.8 High severity
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