macOS Security Mechanism Undermined by Scoped Bookmark Exploit
A newly uncovered flaw in macOS reveals that attackers can bypass the operating system’s App Sandbox by exploiting a loophole in how persistent file access permissions—known as security-scoped bookmarks—are managed.
Cataloged as CVE-2025-31191, this critical vulnerability allows adversaries to tamper with a protected system credential, specifically by removing and substituting keychain entries essential for secure file authentication. In doing so, the exploit effectively dismantles a key integrity layer in macOS’s app isolation model.
At the heart of the issue lies Apple’s scoped bookmark mechanism, a feature intended to let sandboxed apps maintain file access across sessions without breaching privacy constraints. These bookmarks encapsulate permission tokens secured using HMAC-SHA256, where each token’s secret is tied to the app’s unique bundle identifier.
Microsoft researchers, who conducted an in-depth investigation, found that while macOS does restrict reading of these secrets via access control lists (ACLs), the same protection does not extend to deletion or substitution. This oversight opens the door for malicious apps to wipe the legitimate token and replace it with one under their control, complete with permissive ACLs to grant illicit access.
“This exploit enables threat actors to overwrite the ScopedBookmarkAgent’s signing secret, essentially redefining what the system considers trusted access,” the report states.
The breach doesn’t rely on exploiting memory corruption or kernel flaws—it targets a logic error in keychain item enforcement, highlighting how attackers can achieve privilege escalation by manipulating trust models rather than bypassing them entirely.
Exploitation of Compromised Signing Key Facilitates Unauthorized Access
Once an attacker gains control of the signing key, they can perform the following actions:
- Derive the cryptographic signing key associated with any app, using only its bundle ID.
- Create malicious bookmarks that link to arbitrary files, circumventing the intended sandbox restrictions.
- Insert these fabricated bookmarks into the system’s
securebookmarks.plistfile, effectively embedding them into the system’s trusted store.
As a result, when the affected app tries to access files through these tainted bookmarks, the ScopedBookmarkAgent erroneously validates the attacker’s fake credentials, granting unrestricted access without needing the user’s approval.
This flaw nullifies the protections of the app sandbox, providing attackers with an entry point to sensitive system files and the potential for further malicious actions within the compromised environment.
Proof-of-Concept Reveals Office Macro as an Attack Vector, but Vulnerability Impacts All Sandboxed Apps Using Scoped Bookmarks
Microsoft’s proof-of-concept highlights how an attacker could exploit this flaw through a malicious Office macro. However, this issue extends beyond Office applications, affecting any sandboxed program that relies on security-scoped bookmarks to manage file access.
| Risk Factors | Details |
|---|---|
| Affected Platforms | macOS Ventura 13.7.5, tvOS 18.4, iOS 18.4, iPadOS 18.4, macOS Sequoia 15.4, macOS Sonoma 14.7.5 |
| Potential Impact | Mismanagement of system states, leading to unauthorized access to sensitive data; sandbox bypass resulting in arbitrary file access; privilege escalation |
| Exploitation Conditions | Code must first run within a sandboxed app context; user must enable Office macros; administrator privileges are not required |
| CVSS 3.1 Rating | 5.5 (Medium) |
Impacted Systems and Recommended Actions
A range of Apple platforms are affected by this vulnerability, including macOS Ventura, macOS Sequoia, macOS Sonoma, iOS, iPadOS, and tvOS.
This security flaw opens the door for unauthorized access to private user information and may allow for the execution of malicious code with escalated privileges.
Apple has responded by enhancing state management processes in recent security patches. Users are strongly advised to install these critical updates as soon as possible:
- macOS Sequoia 15.4
- macOS Sonoma 14.7.5
- macOS Ventura 13.7.5
- iOS 18.4 and iPadOS 18.4
- tvOS 18.4
For organizations, Microsoft Defender for Endpoint offers detection capabilities for suspicious activity related to keychain tampering, bolstering security defenses.
Jonathan Bar Or of Microsoft Threat Intelligence highlighted the vital role of collaborative efforts across the tech industry to identify and address emerging threats.
This case serves as a reminder of the evolving tactics used by attackers to bypass sandbox defenses, underscoring the critical need for timely security patches and robust endpoint protection.
