CVE-2021-21017

What is this vulnerability?

CVE-2021-21017 is categorized as a high Heap-based Buffer Overflow flaw with a CVSS base score of 8.8. Based on our vulnerability intelligence, this issue occurs when the application fails to securely handle untrusted data boundaries.

Acrobat Reader DC versions versions 2020.013.20074 (and earlier), 2020.001.30018 (and earlier) and 2017.011.30188 (and earlier) are affected by a heap-based buffer overflow vulnerability. An unauthenticated attacker could leverage this vulnerability to achieve arbitrary code execution in the context of the current user. Exploitation of this issue requires user interaction in that a victim must open a malicious file.

This architectural defect enables adversaries to bypass intended security controls, directly manipulating the application's execution state or data layer. Immediate strategic intervention is required.

Risk Assessment

Impact on Systems

✅ Remote Code Execution: Attackers can overwrite the instruction pointer to redirect execution to malicious shellcode.

✅ Memory Corruption: Overwriting adjacent memory regions can corrupt critical application state, leading to privilege escalation.

✅ Denial of Service: Triggering segmentation faults results in immediate disruption of critical systems.

How to Fix and Mitigate CVE-2021-21017

1. Apply Vendor Patches Immediately: This vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog. Apply updates per vendor instructions.
2. Verify Patch Deployment: Confirm all instances are updated using Precogs continuous monitoring.
3. Review Audit Logs: Investigate historical access logs for indicators of compromise related to this attack surface.
4. Implement Defense-in-Depth: Deploy WAF rules, network segmentation, and endpoint detection to limit blast radius.

Defending with Precogs AI

A heap-based buffer overflow in Adobe Acrobat Reader DC allows arbitrary code execution. Attackers deliver a malicious PDF file that overwrites memory bounds during font or image parsing. Precogs Binary SAST engine specifically uncovers memory boundary violations in document renderers.

Use Precogs to continuously scan your codebase, binaries, APIs, and infrastructure for this vulnerability class and related attack patterns. Our AI-powered detection engine combines static analysis with threat intelligence to identify exploitable weaknesses before attackers do.

Start scanning with Precogs →

Vulnerability Code Signature

Attack Data Flow

Vulnerable Code Pattern

// ❌ VULNERABLE: Heap-based Buffer Overflow
void process_data(char *input) {
    char *buffer = malloc(64);
    // Taint sink: copies without bounds checking
    strcpy(buffer, input);
}

Secure Code Pattern

// ✅ SECURE: Bounded copy
void process_data(char *input) {
    char *buffer = malloc(64);
    if (buffer != NULL) {
        // Sanitized boundary check
        strncpy(buffer, input, 63);
        buffer[63] = '\0';
    }
}

How Precogs Detects This

Precogs Binary SAST engine explicitly uncovers memory boundary violations and unsafe memory management functions in compiled binaries.\n