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Introduction
In a major revelation from April 2024, Microsoft’s Threat Intelligence team discovered a macOS vulnerability—later labeled CVE-2025-31191—that could let attackers bypass the operating system’s App Sandbox protections using malicious Office macros. This flaw allowed the exploitation of Apple’s security-scoped bookmarks, providing unauthorized, persistent file access without the user’s knowledge or interaction. In essence, it gave hackers a new route to exfiltrate data, elevate privileges, and run malicious code unrestricted. While Apple patched the flaw in March 2025, the discovery once again illustrates how deeply interconnected vulnerabilities, software design, and user permissions have become across platforms like macOS and Microsoft Office.
This comprehensive breakdown not only uncovers the exploit’s anatomy but also discusses its real-world implications, emphasizing the growing need for sophisticated defense tools, coordinated vulnerability disclosures, and real-time endpoint monitoring.
Breakdown of the macOS CVE-2025-31191 Vulnerability
- In April 2024, Microsoft identified a security flaw in macOS that could allow sandbox escapes through malicious Office macros.
– The flaw exploits
- An attacker could use these bookmarks to bypass macOS sandboxing rules and run unrestricted code on a target device.
- The exploit involved manipulating PLIST files located within the Containers directory, which is exempt from sandbox limitations.
- Attackers don’t need user interaction if they exploit already approved access paths via crafted macro scripts.
- Security-scoped bookmarks are designed to persist file access permissions and use HMAC-SHA256 tokens to secure them.
- Microsoft researchers found a loophole: attackers could delete the existing keychain entry tied to bookmark signing and replace it with one containing a known secret.
- With control over the secret, attackers could sign new bookmarks and gain unauthorized file access permanently.
- The vulnerability was responsibly disclosed to Apple, which issued a fix as CVE-2025-31191 in March 2025.
- Microsoft confirmed the exploit required some complexity but emphasized its potential for privilege escalation and data exfiltration.
- The issue is particularly dangerous for sandboxed apps like Microsoft Word, where users commonly enable macros.
- Apple’s previous hardening of the sandbox mechanism didn’t cover this unique attack vector.
- Microsoft Office APIs like
GrantAccessToMultipleFileswere central to enabling the exploit.
– Attackers abused the trust mechanism in
- Normally, only the ScopedBookmarkAgent has access to the secret signing key stored in macOS Keychain.
– However, the attacker
- This allowed the attacker to generate new valid HMAC tokens for sandbox extension bypass.
- By invoking macros using the modified bookmarks, attackers gained arbitrary file access without further user interaction.
- Microsoft’s threat analysts reverse-engineered sandbox extension mechanisms to build the proof of concept.
- The vulnerability also circumvented the ephemeral nature of kernel tokens by using serialized bookmarks for persistence.
- The research demonstrates how security-scoped bookmarks can be repurposed for malicious persistence if their integrity is compromised.
- Defender for Endpoint was capable of detecting anomalous behavior in sandboxed apps manipulating these security keys.
- Microsoft emphasized the importance of collaboration with Apple and responsible disclosure.
- Beyond macOS, Microsoft also reported other security issues affecting bootloaders and SIP protections, showing a wider pattern of threats.
– The
- Defender for Endpoint blocked the attack by detecting misuse patterns and ACL changes in real time.
- Attackers must bypass several layers of system protection—but this research shows it’s feasible with persistence.
- With each macOS update, attackers find new creative ways to bypass even well-designed safeguards.
- This case study strengthens the argument for zero trust models, advanced behavioral monitoring, and endpoint protection.
- Microsoft’s detection strategies involved catching unauthorized sandboxed app behaviors, such as secret replacement and unapproved file access.
- Researchers stress that even highly sandboxed environments like macOS and Office can become vulnerable with creative exploitation.
- It’s a stark reminder that trusted apps and OS security features can be weaponized against users without active vigilance.
What Undercode Say:
Microsoft’s uncovering of CVE-2025-31191 showcases an intersection of deep system internals, creative abuse of inter-process communication, and the clever repurposing of legitimate macOS features like security-scoped bookmarks. The real danger lies not in the theoretical aspects of the exploit, but in its practical application—crafted Office macros that, once triggered, allow silent sandbox escape.
macOS sandboxing is designed to isolate apps and prevent them from affecting system-wide operations or accessing other data. However, its reliance on kernel-generated tokens and trusted user approvals creates a security model that’s only as strong as its weakest trust mechanism. ScopedBookmarkAgent was supposed to protect long-term access permissions, but the ability to replace its keychain secrets entirely undermines its trust model.
The exploit’s brilliance lies in its non-invasive approach: rather than hacking into Apple’s systems directly, it simply erases and redefines them. The attacker doesn’t need the keychain secret—they just need the ability to overwrite it. That is not only easier but more stealthy.
Security-scoped bookmarks are an elegant solution for user convenience, but when combined with Microsoft Office’s sandbox-aware APIs, they offer attackers a pathway to misuse. GrantAccessToMultipleFiles becomes the lever through which arbitrary access is achieved once the integrity of the bookmarks is compromised.
Reverse engineering the entire security path—from Open dialog box to persistent file access tokens—reveals a systemic vulnerability. This attack chain could be repurposed across apps using similar APIs, making this exploit potentially generic for any macOS sandboxed application leveraging bookmarks.
Apple’s fix in March 2025 was swift, but the issue exposes a larger truth: sophisticated attackers don’t just break in; they reroute legitimate mechanisms to gain access. The ability to manipulate PLIST files, manage keychain ACLs, and simulate cryptographic signatures opens a host of possible attack vectors for both current and future threats.
Microsoft’s disclosure also exemplifies why modern cybersecurity must be layered. Endpoint security software that analyzes behavior in real time—such as detecting an Office macro attempting to access system-level keychains—is essential in catching these anomalies.
Even more important is the principle of responsible disclosure. By informing Apple, Microsoft ensured that the wider user base is protected, despite the exploit’s complexity. This speaks volumes about how the security community must function—competitors during the day, collaborators when the stakes are user safety.
In the context of broader threats Microsoft has disclosed—from kernel-level rootkits to bootloader bypasses—this vulnerability represents a deeply technical but highly relevant example of what persistent attackers can achieve. The lesson here is sobering: even the best-designed safeguards can be outmaneuvered when permissions, user trust, and persistent tokens mix.
It reinforces the need for software vendors to constantly re-audit security models, not only for flaws but for trust-based systems that can be hijacked by state or criminal actors. Whether it’s a well-sandboxed Office macro or a bootloader vulnerability, today’s exploits are exploiting assumptions, not just bugs.
This underscores why endpoint detection, behavioral analytics, and AI-assisted threat intelligence must be core components of enterprise and consumer defense strategies. Microsoft’s own Defender platform caught the behavior by detecting deviations in expected macro behavior, reinforcing the value of machine learning in security monitoring.
CVE-2025-31191 should be seen as a milestone vulnerability—not just for what it allowed but for how it reshaped the way we think about cross-platform security boundaries. Apple’s systems were strong, but not infallible. And Microsoft’s insight made all the difference.
Fact Checker Results:
- ✅ Apple officially patched the CVE-2025-31191 vulnerability on March 31, 2025.
- ✅ The flaw centered around the abuse of security-scoped bookmarks and keychain entries.
- ✅ Microsoft’s Defender for Endpoint can detect and block the exploit’s behavioral patterns.
Prediction
In the aftermath of CVE-2025-31191, Apple is likely to tighten the cryptographic control over security-scoped bookmarks and their corresponding keychain entries. Future macOS updates may introduce stricter sandbox verification, revamp how access tokens are stored, or even limit how persistent file access is granted. Security vendors will increasingly monitor keychain manipulation patterns, and cross-platform defense collaboration between tech giants will become standard protocol in anticipating threats of this complexity.
References:
Reported By: www.microsoft.com
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