iOS and iPadOS: Concurrent Execution using Shared Resource with Improper Synchronization
CVE-2026-20677 is a critical-severity concurrent execution using shared resource with improper synchronization vulnerability in iOS and iPadOS from Apple, with a CVSS 3.1 base score of 9.0 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 18.7.5, 26.3 as the first without the flaw, so updating iOS and iPadOS to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.32% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update iOS and iPadOS to 18.7.5 or 26.3, whichever matches your release line, or a later version.
- Update macOS to 14.8.4 or 15.7.4 or 26.3, whichever matches your release line, or a later version.
- Update visionOS to 26.3 or a later version.
- Read the advisory on support.apple.com for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Apple | iOS and iPadOS | before 18.7.5; before 26.3 | 18.7.5, 26.3 |
| Apple | macOS | before 14.8.4; before 15.7.4; before 26.3 | 14.8.4, 15.7.4, 26.3 |
| Apple | visionOS | before 26.3 | 26.3 |
| Apple | iPadOS | before 18.7.5; 26.0 up to, but not including, 26.3 | 18.7.5, 26.3 |
| Apple | Iphone OS | before 18.7.5; 26.0 up to, but not including, 26.3 | 18.7.5, 26.3 |
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
- HighSuccess depends on conditions outside the attacker's control.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- ChangedThe attack can reach beyond the vulnerable component into other systems.
- 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:H/PR:N/UI:N/S:C/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 9.0 | Critical | NVD |
| CVSS 3.1 | 9.0 | Critical | CISA (ADP) |
Official description
A race condition was addressed with improved handling of symbolic links. This issue is fixed in iOS 18.7.5 and iPadOS 18.7.5, iOS 26.3 and iPadOS 26.3, macOS Sequoia 15.7.4, macOS Sonoma 14.8.4, macOS Tahoe 26.3, visionOS 26.3. A shortcut may be able to bypass sandbox restrictions.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Concurrent Execution using Shared Resource with Improper Synchronization
The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.
How developers prevent this class of flaw
- In languages that support it, use synchronization primitives. Only wrap these around critical code to minimize the impact on performance.
- Use thread-safe capabilities such as the data access abstraction in Spring.
- Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring. Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Advisories
- support.apple.com/en-us/126346Release Notes
- support.apple.com/en-us/126347Release Notes
- support.apple.com/en-us/126348Release Notes
- support.apple.com/en-us/126350Release Notes
- support.apple.com/en-us/126353Release Notes
Other references
Other vulnerabilities in iOS and iPadOS
- 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 Concurrent Execution using Shared Resource with Improper Synchronization vulnerabilities
- 7.0 High severity
- 7.5 High severity
- 7.0 High severity
- 7.0 High severity
- 7.8 High severity
- 7.9 High severity
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