CVE-2026-81977: Adobe Acrobat Information Disclosure Flaw

CVE-2026-81977 Overview

CVE-2026-81977 is an integer underflow vulnerability [CWE-191] in Adobe Acrobat and Acrobat Reader. The flaw allows attackers to disclose sensitive process memory when a victim opens a crafted PDF file. Adobe published an advisory tracked as APSB26-141 describing the issue and affected releases.

The vulnerability affects Adobe Acrobat (Classic track), Acrobat DC (Continuous), and Acrobat Reader DC across Windows and macOS. Exploitation requires user interaction, and the attack executes in the local user context. While the flaw does not permit direct code execution, leaked memory can expose secrets, tokens, or addresses useful for bypassing exploit mitigations.

Critical Impact
An attacker who convinces a user to open a malicious PDF can read sensitive memory from the Acrobat process, potentially exposing credentials, session data, or information usable to chain further exploits.

Affected Products

Adobe Acrobat (Classic track)
Adobe Acrobat DC and Acrobat Reader DC (Continuous track)
Adobe Acrobat and Reader on Microsoft Windows and Apple macOS

Discovery Timeline

2026-09-08 - CVE-2026-81977 published to the National Vulnerability Database
2026-09-10 - Record last modified in NVD

Technical Details for CVE-2026-81977

Vulnerability Analysis

The issue is classified as an Integer Underflow (Wrap or Wraparound) weakness [CWE-191]. Acrobat parses PDF structures whose size or length fields drive downstream memory operations. When a crafted value causes an arithmetic operation to wrap below zero, the resulting unsigned value becomes very large.

Acrobat then treats that wrapped value as a valid length for a read operation. The read traverses past the intended buffer boundary and returns adjacent heap or stack contents to attacker-controlled logic inside the document. That data can be exfiltrated through embedded scripting, form fields, or side-channel behaviors within the PDF renderer.

Because the vulnerability yields information disclosure rather than control-flow hijack, it is well-suited as a precursor stage. Attackers commonly pair such leaks with a separate memory corruption bug to defeat Address Space Layout Randomization (ASLR).

Root Cause

The root cause is unchecked signed-to-unsigned conversion or subtraction on a length field parsed from an untrusted PDF object. The code path fails to validate that the operand is greater than or equal to the value being subtracted before using the result as a buffer size.

Attack Vector

Delivery relies on social engineering. An attacker distributes a malicious PDF through email, chat, or a compromised website. When the victim opens the file in a vulnerable Acrobat build, the parser processes the malformed structure and leaks memory contents accessible to the reader process. See the Adobe Acrobat Security Advisory APSB26-141 for technical details.

Detection Methods for CVE-2026-81977

Indicators of Compromise

PDF files delivered through email or web downloads that contain malformed length fields, unusual embedded JavaScript, or heap-grooming object streams.
Acrobat or Reader processes reading unusually large object streams shortly after a PDF is opened.
Outbound network connections from AcroRd32.exe or Acrobat.exe to untrusted destinations immediately following document open events.

Detection Strategies

Inspect PDFs at the mail gateway for anomalous object stream sizes and mismatched cross-reference table entries.
Correlate Acrobat process telemetry with parent processes such as Outlook, browsers, or chat clients to flag phishing-driven opens.
Hunt for Acrobat processes spawning script hosts or making DNS lookups to newly registered domains.

Monitoring Recommendations

Enable process command-line and child-process logging for Acrobat.exe and AcroRd32.exe on Windows endpoints.
Collect endpoint telemetry into a central data lake to correlate document-open events with subsequent network egress.
Track Acrobat build versions across the fleet to identify hosts that have not received the APSB26-141 update.

How to Mitigate CVE-2026-81977

Immediate Actions Required

Apply the Adobe update referenced in advisory APSB26-141 to all Acrobat and Acrobat Reader installations on Windows and macOS.
Prioritize patching for users who routinely open PDFs from external senders, including finance, HR, and executive assistants.
Reinforce user awareness that PDFs from unverified senders should be opened only in sandboxed or web-based viewers.

Patch Information

Adobe released fixed builds for both the Classic and Continuous tracks of Acrobat and Acrobat Reader. Refer to the Adobe Acrobat Security Advisory APSB26-141 for the specific fixed version numbers and download locations. Deploy updates through managed software distribution to ensure coverage of both DC and Classic installations.

Workarounds

Enable Protected View and Protected Mode in Acrobat and Reader to sandbox the parser process until patches are applied.
Disable JavaScript execution within Acrobat through the Preferences dialog or enterprise policy to reduce exfiltration primitives.
Route inbound PDFs through a rendering gateway that converts documents to images or sanitized PDFs before delivery to end users.

bash

# Configuration example: disable Acrobat JavaScript via Windows registry (per-user)
reg add "HKCU\Software\Adobe\Acrobat Reader\DC\JSPrefs" /v bEnableJS /t REG_DWORD /d 0 /f

# Enforce Protected View for files from untrusted locations
reg add "HKCU\Software\Adobe\Acrobat Reader\DC\TrustManager" /v iProtectedView /t REG_DWORD /d 2 /f