Security readout for executives and security teams
Plain-English summary
This is a low-severity Adobe Acrobat Reader DC flaw that can expose limited information when a user opens a malicious file. It is not described as remotely exploitable without user interaction, and the bundle does not show known active exploitation.
Executive priority
Handle through normal endpoint patching. It deserves completion because Acrobat is widely used, but available evidence supports low urgency rather than emergency response.
Technical view
CVE-2021-21089 is a CWE-125 out-of-bounds read in Acrobat Reader DC URI parsing. Affected versions include 2020.013.20074 and earlier, 2020.001.30018 and earlier, and 2017.011.30188 and earlier. CVSS 3.1 is 3.3 with local attack vector and required user interaction.
Likely exposure
Exposure is most likely on workstations running affected Acrobat Reader DC versions where users open untrusted PDFs or files. It is not presented as a server-side or internet-facing exposure.
Exploitation context
The source bundle says exploitation requires a victim to open a malicious file. It does not cite CISA KEV listing, public exploitation, exploit code, or confirmed real-world abuse.
Researcher notes
The bundle identifies URI parsing and CWE-125 but does not provide root-cause detail, crash conditions, fixed build numbers, or exploitation telemetry. Treat exploitability conclusions as limited to user-assisted local file opening.
Mitigation direction
- Inventory Acrobat Reader DC versions across managed endpoints.
- Follow Adobe APSB21-09 and deploy the applicable Reader update.
- Prioritize users who handle external documents frequently.
- Maintain controls that warn on suspicious attachments and downloads.
Validation and detection
- Confirm installed Reader versions are newer than affected builds.
- Check whether endpoints still run the 2017, 2020 Classic, or 2020 Continuous affected branches.
- Review patch management records against Adobe APSB21-09.
- Do not validate with malicious files in production environments.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-125: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-21089 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- Low
- CVSS
- 3.3 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N1.81.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
3.3LowVector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N
Source materials
- CVE List V5 sourceCVE List V5
- https://helpx.adobe.com/security/products/acrobat/apsb21-09.htmlCVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Out-of-bounds Read
Out-of-bounds Read represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.