CVE-2025-21156 Overview
CVE-2025-21156 is an integer underflow vulnerability [CWE-191] affecting Adobe InCopy versions 20.0, 19.5.1, and earlier. The flaw enables arbitrary code execution in the context of the current user when a victim opens a crafted file. Adobe disclosed the issue in security bulletin APSB25-10 and assigned a CVSS v3.1 base score of 7.8. Exploitation requires user interaction, limiting opportunistic abuse but aligning with phishing and social engineering workflows. Attackers commonly weaponize document-handling flaws of this class to deliver follow-on payloads after initial document execution.
Critical Impact
Successful exploitation grants arbitrary code execution with the privileges of the user running InCopy, enabling payload installation, credential theft, and lateral movement.
Affected Products
- Adobe InCopy 20.0
- Adobe InCopy 19.5.1 and earlier
- Adobe InCopy on Apple macOS and Microsoft Windows
Discovery Timeline
- 2025-02-11 - CVE-2025-21156 published to NVD
- 2025-03-03 - Last updated in NVD database
Technical Details for CVE-2025-21156
Vulnerability Analysis
The vulnerability resides in Adobe InCopy's handling of file structures during document parsing. An integer underflow [CWE-191] occurs when arithmetic on an unsigned value wraps below zero, producing an unexpectedly large result. InCopy then uses that wrapped value as a size, offset, or loop bound during memory operations.
The miscalculation drives out-of-bounds memory access or undersized buffer allocations. Attackers leverage this corruption to overwrite adjacent memory structures, including function pointers or object metadata. Controlled corruption ultimately redirects execution to attacker-supplied shellcode within the InCopy process.
Exploitation runs in the security context of the logged-in user. On standard workstations, that context includes access to documents, network shares, and authenticated cloud sessions. The local attack vector combined with required user interaction places this issue squarely in the malicious document delivery category.
Root Cause
The root cause is an unchecked arithmetic operation on a length or size field parsed from an InCopy document. When attacker-supplied input drives the operand below zero, the resulting wraparound bypasses subsequent bounds checks and corrupts heap state.
Attack Vector
An attacker crafts a malicious InCopy document and delivers it through email, file sharing, or a compromised website. When the victim opens the file in a vulnerable InCopy build, the underflow triggers during parsing and executes the embedded payload. No authentication or network access to the host is required.
No public proof-of-concept code is available. See the Adobe Security Advisory APSB25-10 for vendor-provided technical context.
Detection Methods for CVE-2025-21156
Indicators of Compromise
- Unexpected child processes spawned by InCopy.exe or the macOS InCopy binary, particularly shells, scripting interpreters, or rundll32.exe.
- InCopy process crashes with access violations referencing heap corruption during document open operations.
- InCopy writing executable files or scripts to user-writable directories such as %TEMP% or ~/Library/Caches.
- Network connections initiated by InCopy to non-Adobe domains following document open events.
Detection Strategies
- Monitor process lineage for InCopy spawning unexpected children and alert on suspicious command lines.
- Correlate InCopy file-open telemetry with subsequent file writes to executable extensions or autorun locations.
- Hunt for InCopy memory anomalies and crash dumps that indicate exploitation attempts against the parsing code path.
Monitoring Recommendations
- Forward endpoint process, file, and network telemetry from workstations running Adobe Creative Cloud applications to a centralized analytics platform.
- Alert on InCopy document downloads from external email or web sources prior to first open.
- Track InCopy version inventory across the fleet to identify hosts still running 20.0 or 19.5.1 and earlier.
How to Mitigate CVE-2025-21156
Immediate Actions Required
- Apply the Adobe InCopy security updates referenced in APSB25-10 to all affected Windows and macOS endpoints.
- Identify and prioritize patching of systems used to process InCopy files received from external parties.
- Restrict opening of .icml and related InCopy documents originating from untrusted sources until patches are applied.
Patch Information
Adobe released fixed versions for InCopy on Windows and macOS. Refer to the Adobe Security Advisory APSB25-10 for exact patched build numbers and download locations. Deploy updates through Adobe Creative Cloud Desktop or enterprise software distribution tooling.
Workarounds
- Block inbound InCopy document attachments at the email gateway until patching completes.
- Run InCopy under standard user accounts without local administrator rights to limit post-exploitation impact.
- Enable operating system exploit mitigations such as Windows Defender Exploit Guard and macOS Gatekeeper enforcement.
# Verify installed Adobe InCopy version on Windows
reg query "HKLM\SOFTWARE\Adobe\InCopy" /s | findstr /i version
# Verify installed Adobe InCopy version on macOS
mdls -name kMDItemVersion "/Applications/Adobe InCopy 2024/Adobe InCopy 2024.app"
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
