CVE-2025-43400 Overview
CVE-2025-43400 is an out-of-bounds write vulnerability affecting multiple Apple operating systems including iPadOS, iOS, macOS, and visionOS. The vulnerability exists in the font processing component where insufficient bounds checking allows a maliciously crafted font file to trigger memory corruption. When exploited, this flaw can lead to unexpected application termination or corrupt process memory, potentially enabling further exploitation.
Critical Impact
Processing a maliciously crafted font may lead to unexpected app termination or corrupt process memory, affecting application stability and potentially enabling code execution.
Affected Products
- Apple iPadOS (versions prior to 26.1)
- Apple iOS/iPhone OS (versions prior to 26.1)
- Apple macOS (versions prior to 26.1)
- Apple visionOS (versions prior to 26.1)
- Apple watchOS (versions prior to 26.1)
- Apple tvOS (versions prior to 26.1)
Discovery Timeline
- September 29, 2025 - CVE-2025-43400 published to NVD
- November 4, 2025 - Last updated in NVD database
Technical Details for CVE-2025-43400
Vulnerability Analysis
This vulnerability is classified as CWE-787 (Out-of-Bounds Write), a memory corruption vulnerability that occurs when a program writes data past the end of or before the beginning of an intended buffer. In the context of CVE-2025-43400, the flaw resides in Apple's font parsing subsystem, which fails to properly validate boundaries when processing font file data structures.
The attack can be initiated remotely via the network but requires user interaction—such as opening a document containing a malicious embedded font or visiting a webpage that loads a crafted font file. Successful exploitation can corrupt process memory, leading to denial of service through application crashes. In more sophisticated attack scenarios, memory corruption vulnerabilities of this nature can potentially be chained with other techniques to achieve arbitrary code execution.
Root Cause
The root cause is improper bounds checking during font data processing. When parsing font tables or glyph data, the affected code fails to validate that write operations stay within allocated buffer boundaries. This allows attacker-controlled data from the malicious font file to overwrite adjacent memory regions, corrupting process memory and potentially overwriting critical data structures.
Attack Vector
The vulnerability is exploitable via network-based attack vectors where an attacker delivers a maliciously crafted font file to the victim. Attack scenarios include:
- Embedding a malicious font in a document (PDF, Word, web page) that the victim opens
- Hosting a malicious web font on an attacker-controlled website that the victim visits
- Sending a malicious font file directly via email or messaging platforms
The attack requires user interaction to trigger font processing. Once the malicious font is processed by the operating system's font rendering subsystem, the out-of-bounds write condition is triggered, resulting in memory corruption. This vulnerability affects the core font processing components shared across Apple's ecosystem, making iOS, iPadOS, macOS, watchOS, tvOS, and visionOS all susceptible.
Detection Methods for CVE-2025-43400
Indicators of Compromise
- Unexpected application crashes when opening documents or web pages containing custom fonts
- Memory corruption errors in system logs related to font rendering or CoreText components
- Unusual font files with malformed or oversized table entries in temporary directories
- Repeated crashes in apps that process embedded fonts (Safari, Mail, Preview, etc.)
Detection Strategies
- Monitor for application crashes with signatures indicating memory corruption in font processing libraries
- Implement endpoint detection rules to identify suspicious font file access patterns
- Review system crash logs for CoreText, FontParser, or related framework errors
- Deploy behavioral analysis to detect anomalous memory access patterns during document rendering
Monitoring Recommendations
- Enable enhanced crash reporting to capture memory corruption events
- Monitor file system activity for newly written font files from untrusted sources
- Track network connections that download font resources from suspicious domains
- Configure SentinelOne agents to alert on exploitation attempts targeting font processing components
How to Mitigate CVE-2025-43400
Immediate Actions Required
- Update all Apple devices to the latest patched versions: watchOS 26.1, tvOS 26.1, and corresponding updates for iOS, iPadOS, macOS, and visionOS
- Enable automatic updates on all Apple devices to receive security patches promptly
- Exercise caution when opening documents or visiting websites from untrusted sources
- Consider disabling automatic font loading in browsers and document viewers where possible
Patch Information
Apple has addressed this vulnerability with improved bounds checking in the font processing code. The fix is included in watchOS 26.1 and tvOS 26.1, with corresponding patches available for other affected platforms. Users and administrators should apply these updates immediately.
For detailed patch information, refer to the official Apple security advisories:
Additional disclosure information is available via the Full Disclosure mailing list.
Workarounds
- Restrict access to untrusted font files and documents containing embedded fonts
- Configure web browsers to block custom web fonts from untrusted domains
- Implement network-level filtering to block downloads of potentially malicious font files
- Use application sandboxing and memory protection features available in enterprise management tools
# Verify Apple device software versions
# On macOS, check the current version:
sw_vers -productVersion
# On iOS/iPadOS, verify via Settings > General > About > Software Version
# Ensure version 26.1 or later is installed
# For enterprise environments, use MDM to enforce updates:
# Example: Jamf Pro policy to require minimum OS version
# Minimum macOS Version: 26.1
# Minimum iOS Version: 26.1
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
