CVE-2021-21042
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedAcrobat Reader DC versions 2020.013.20074 (and earlier), 2020.001.30018 (and earlier) and 2017.011.30188 (and earlier) are affected by an Out-of-bounds Read vulnerability that could lead to arbitrary disclosure of information in the memory stack. An attacker could leverage this vulnerability to bypass mitigations such as ASLR. Exploitation of this issue requires user interaction in that a victim must open a malicious file.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceOut-of-bounds Read vulnerability in Adobe Acrobat Reader DC allowing arbitrary memory stack disclosure. Exploitation requires user to open a malicious PDF file, enabling information disclosure that could be leveraged to bypass ASLR mitigation.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data>= 17.0, <= 17.011.30188>= 20.0, <= 20.001.30018<= 20.013.20074>= 17.0, <= 17.011.30188>= 20.0, <= 20.001.300183<= 20.013.20074CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- Required
- Scope
- Unchanged
- Confidentiality
- High
- Integrity
- None
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify installed Adobe Acrobat or Reader versionOpen the application, then go to Help > About Adobe Acrobat Reader (or About Adobe Acrobat). Alternatively, on Windows, right-click the executable (AcroRd32.exe or AcroTray.exe) in Program Files, select Properties, and check the File version tab.Affected if The displayed version falls within 17.0 to 17.011.30188, 20.0 to 20.001.30018 (or 20.001.300183), or is 20.013.20074 or lower for DC variants.
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Confirm product variant and build typeCheck whether the installation is Adobe Acrobat or Adobe Acrobat Reader, and whether it is the Continuous (DC) track or Classic track. This is visible in the About dialog or in the application name under Programs and Features.Affected if The product is any DC variant with version 20.013.20074 or below, regardless of the Classic track version being in the affected range.
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Verify PDF file handling is activeConfirm that the Adobe Acrobat or Reader application is configured as the default PDF handler, or that users routinely open PDF files using the installed application. Check default application settings in Windows or inspect file associations.Affected if The application processes PDF files as a default handler or is used to open untrusted PDF documents, creating the exploitation vector.
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Review recent PDF opening activity (optional)Examine browser download history, email attachments, or local file access logs for recently opened PDF files. This can indicate potential exposure if any originated from untrusted sources.Affected if Users have opened PDF files from unknown or untrusted sources while running a vulnerable version, which is the required user interaction for exploitation.
A user is affected if their installed Adobe Acrobat or Reader version matches any of the specified vulnerable ranges and they open or process PDF files with the application.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataUpdate Adobe Acrobat Reader DC to a patched version beyond 2020.013.20074, 2020.001.30018, or 2017.011.30188. User awareness to avoid opening untrusted PDF files reduces exploitation likelihood.
- Consultation1.0 h
- Implementation1.0 h
- Testing2.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-21042 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-21042 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.
- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
- No spam, self-promotion, credentials, or personal data