New Apple CPU Side-Channel Attacks Steal Data from Browsers

A team of security researchers has uncovered new side-channel vulnerabilities in modern Apple processors, capable of stealing sensitive information from web browsers. The vulnerabilities, identified as FLOP and SLAP, highlight flaws in Apple’s speculative execution mechanisms, allowing attackers to extract private data remotely.

The research was conducted by teams from the Georgia Institute of Technology and Ruhr University Bochum. These experts previously disclosed a similar attack called ‘iLeakage’ in October 2023. Their latest findings, detailed in two separate papers, demonstrate how Apple’s CPU architecture is vulnerable to side-channel exploitation.

Understanding the Vulnerabilities

Both FLOP and SLAP attacks stem from weaknesses in Apple’s speculative execution implementation, similar to previous attacks like Spectre and Meltdown. Speculative execution is a technique used to predict and execute future instructions in advance, improving CPU performance. However, flaws in its design can inadvertently leak sensitive data.

“Starting with the M2/A15 generation, Apple CPUs attempt to predict the next memory address that will be accessed by the core,” the researchers explained. “Moreover, starting with the M3/A17 generation, they attempt to predict the data value that will be returned from memory. However, mispredictions in these mechanisms can result in arbitrary computations being performed on out-of-bounds data or wrong data values.”

These mispredictions have severe security implications, potentially allowing attackers to bypass web browser protections and access cross-origin data, such as personal details stored in Safari and Chrome.

How FLOP and SLAP Attacks Work

These attacks exploit Apple’s predictive memory mechanisms in distinct ways:

FLOP (False Load Output Prediction)

FLOP specifically affects Apple’s latest M3, M4, and A17 processors. The attack manipulates Apple’s Load Value Prediction (LVP), which anticipates memory values before actual retrieval. When the prediction is incorrect, the CPU temporarily processes incorrect data, creating an opportunity for attackers to extract sensitive information.

Researchers demonstrated the FLOP attack by training the M3 CPU to anticipate specific values. Once mispredictions occur, attackers can measure cache timing and extract leaked data before the CPU corrects itself.

The impact of FLOP includes:

Escaping Safari’s sandbox.

Stealing sender and subject details from Proton Mail inboxes.

Extracting location history from Google Maps.

Recovering private events from iCloud Calendar.

SLAP (Speculative Load Address Prediction)

SLAP affects Apple’s M2 and A15 processors, targeting Load Address Prediction (LAP). Instead of predicting memory values, LAP guesses which memory address will be accessed next. Attackers can train the CPU into following a specific pattern, then manipulate its memory layout, causing it to mistakenly access sensitive data.

Since the CPU trusts its prediction, it processes sensitive information before realizing the mistake. This allows attackers to infer leaked data through cache timing analysis.

Demonstrated SLAP attack outcomes include:

Retrieving Gmail inbox data.

Extracting Amazon order history and browsing details.

Tracking Reddit user activity.

Real-World Implications

FLOP and SLAP attacks are concerning because they can be executed remotely through a web browser. A victim simply visiting a malicious website is enough for sensitive information to be leaked, bypassing traditional security barriers such as browser sandboxing, Address Space Layout Randomization (ASLR), and memory protections.

Unlike traditional cyber threats, these attacks do not rely on malware. Instead, they leverage JavaScript and WebAssembly scripts to manipulate Apple’s speculative execution flaws. This makes detection and mitigation significantly more challenging.

Apple’s Response and Current Security Measures

Researchers disclosed the vulnerabilities to Apple in two stages:

SLAP was reported on March 24, 2024.

FLOP was reported on September 3, 2024.

Apple acknowledged the proof-of-concept and expressed gratitude for the research, stating that it aids in better understanding such threats. However, as of now, Apple has not released a fix for these vulnerabilities.

“We want to thank the researchers for their collaboration as this proof of concept advances our understanding of these types of threats,” Apple stated. “Based on our analysis, we do not believe this issue poses an immediate risk to our users.”

Despite Apple’s assessment, researchers emphasize that these flaws pose a significant risk due to their ability to extract private data remotely and invisibly.

Mitigation Strategies for Users

Since Apple has yet to release patches, users concerned about these vulnerabilities can take the following steps:

Disable JavaScript in Safari and Chrome — Since these attacks exploit JavaScript-based code execution, disabling JavaScript can prevent exploitation. However, this may disrupt many websites.

Use Alternative Browsers — If concerned about Safari’s security, switching to browsers with enhanced sandboxing protections may reduce exposure.

Keep Software Updated — Regularly updating macOS and iOS ensures users receive security patches as soon as Apple releases them.

Use Security Extensions — Browser extensions that block JavaScript execution, such as NoScript or uBlock Origin, can help minimize the attack surface.

Limit Exposure to Untrusted Websites — Avoiding unfamiliar websites and clicking on suspicious links reduces the likelihood of encountering malicious scripts designed to exploit these vulnerabilities.

What’s Next?

Security experts anticipate that Apple will address these flaws in upcoming macOS and iOS updates. Until then, users must take proactive steps to mitigate risks. Meanwhile, researchers continue to analyze Apple’s CPU architecture, seeking additional vulnerabilities that may exist in speculative execution mechanisms.

Given the high stakes associated with these attacks — ranging from email leaks to tracking browsing behavior — security professionals urge Apple to prioritize a fix. As previous speculative execution flaws like Spectre and Meltdown demonstrated, such vulnerabilities can have long-term security implications if left unpatched.

While Apple downplays the immediate risk, the ability of FLOP and SLAP attacks to steal personal information remotely raises concerns among security researchers and privacy advocates. The coming months will determine how Apple addresses these threats and whether additional mitigations are required.

For now, users are advised to remain vigilant, apply available security settings, and stay informed about potential updates addressing these critical vulnerabilities.