HighCISA KEVExploited in the wildPublic exploit

Heap-based Buffer Overflow RCE in Adobe Acrobat Reader DC

IdentifiersCVE-2021-21017CWE-122· Heap-based Buffer Overflow

CVE-2021-21017 is a heap-based buffer overflow vulnerability affecting Adobe Acrobat Reader DC and related supported release lines, including versions 2020.013.20074 and earlier, 2020.001.30018 and earlier, and 2017.011.30188 and earlier. The flaw can be triggered when the application processes a malicious file, causing memory corruption in heap-allocated data structures. A successful exploit can lead to arbitrary code execution in the security context of the current user. The vulnerability was reported as being actively exploited in the wild, with observed exploitation affecting Windows systems, and it also affects Adobe Reader on Windows and macOS.

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ANALYST BRIEF

Impact, mitigation & remediation

What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.

Impact

What an attacker gets, and what they’ve been doing with it.

Successful exploitation allows arbitrary code execution in the context of the user running Adobe Reader or Acrobat. This can enable full compromise of the user session, including execution of attacker-controlled payloads, access to data available to that user, installation of additional malware, and use of the compromised host as a foothold for further intrusion activity. Because exploitation occurs through malicious document handling, it also creates a practical phishing and document-delivery attack vector.

Mitigation

If you can’t patch tonight, do this now.

If immediate patching is not possible, reduce exposure by restricting the opening of untrusted or externally supplied PDF files, especially those delivered through email or web downloads, and by using application control, endpoint detection, and sandboxing or protected document-handling workflows where available. Because no separate vendor workaround is described, patching remains the primary mitigation.

Remediation

Patch, then assume compromise.

Apply Adobe's official security updates released in APSB21-09 for all affected Adobe Acrobat Reader DC and related supported product versions. Systems should be upgraded to patched releases that address CVE-2021-21017. Priority should be given to internet-exposed user endpoints and high-risk populations that routinely open externally sourced PDF documents.

PUBLIC EXPLOITS

Exploits

1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.

VALID 1 / 1 TOTALView more in app

CVE-2021-21017MaturityPoCVerified exploit

This repository provides a proof-of-concept (PoC) exploit for CVE-2021-21017, a heap overflow vulnerability in Adobe Acrobat Reader (notably version 2020.013.20074, IA32 plugin). The repository contains three files: a JavaScript file (CVE-2021-21017.js) with the exploit logic, a malicious PDF (CVE-2021-21017.pdf) embedding the JavaScript, and a README.md explaining the vulnerability and exploitation technique. The exploit leverages a type confusion in the handling of the PDF's baseURL (when encoded as UTF-16BE), which, when combined with a crafted relative URL and the submitForm API, leads to an out-of-bounds read and heap overflow. The JavaScript performs heap spraying to increase reliability. The attack vector is a malicious PDF file, and the main fingerprintable endpoint is the PDF's BaseURL entry in UTF-16BE. The exploit is a PoC and primarily causes a crash or memory corruption, with no weaponized payload.

ZeusBoxDisclosed Feb 26, 2021javascriptfile

EXPOSURE SURFACE

Affected products & vendors

Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.

VendorProductType

AdobeAcrobatapplication

AdobeAcrobat Dcapplication

AdobeAcrobat Readerapplication

AdobeAcrobat Reader Dcapplication

Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.

ACTIVITY FEED

Recent activity

1 sources tracked across advisories and community write-ups. News coverage will land here when it surfaces.

1 SOURCESView more in app

No news coverage yet. Advisories and community discussion only.

What this page doesn’t show

The version that knows your environment.

This page is what’s public. Mallory adds the parts that aren’t: which of your assets are affected, which adversaries are exploiting it right now, which detections to deploy, and what to do tonight.

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Exposure mapping

Query your assets running an affected version, and investigate the blast radius.

Threat actor evidence

Every observed campaign linking this CVE to a named adversary.

Associated malware

Malware families riding this exploit, with evidence and IOCs.

Detection signatures2

YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.

Vendor-by-vendor mapping

Cross-references every affected SKU, including bundled OEM variants.

Social activity

Community discussion across Reddit, Mastodon, and other social sources.

EXTERNAL REFERENCES

MITRE CVE

cve.org · CVE-2021-21017

NVD

nvd.nist.gov/vuln/detail/CVE-2021-21017

MITRE CWE · CWE-122

Heap-based Buffer Overflow

Vendor Advisory

helpx.adobe.com/security/products/acrobat/apsb21-09.html

Third Party Advisory

cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-21017

Heap-based Buffer Overflow RCE in Adobe Acrobat Reader DC

IdentifiersCVE-2021-21017CWE-122· Heap-based Buffer Overflow