Security readout for executives and security teams
Plain-English summary
This is a low-severity Adobe Acrobat Reader DC issue where opening a malicious file could expose memory information from the current user’s session. It is not described as remote code execution, and the sources do not show active exploitation.
Executive priority
Handle through routine patch management unless affected Acrobat Reader DC versions are widespread in high-risk user groups. The issue is low severity but still relevant because exploitation depends on normal user file-opening behavior.
Technical view
CVE-2021-39858 is a CWE-125 out-of-bounds read in PostScript file parsing affecting Acrobat Reader DC 2021.005.20060 and earlier, 2020.004.30006 and earlier, and 2017.011.30199 and earlier. CVSS is 3.3: local attack vector, no privileges, user interaction required, confidentiality impact only.
Likely exposure
Exposure is most likely on endpoints with affected Acrobat Reader DC versions where users can open files from email, web downloads, or shared storage. Business impact is limited to potential current-user memory disclosure, based on the provided sources.
Exploitation context
The provided sources say exploitation requires a victim to open a malicious file. CISA KEV status is false in the bundle, and no cited source here supports active exploitation.
Researcher notes
The source bundle identifies memory disclosure only, not integrity or availability impact. Product naming is not perfectly consistent: the title references Acrobat Pro DC, while the description and affected entry reference Acrobat Reader DC.
Mitigation direction
- Check Adobe APSB21-55 for fixed versions and vendor deployment guidance.
- Identify Acrobat Reader DC installs at or below the affected version ranges.
- Apply Adobe-supported updates through normal endpoint management channels.
- Reduce user exposure to untrusted files until affected clients are updated.
Validation and detection
- Inventory Acrobat Reader DC versions across managed endpoints.
- Confirm whether any install matches the listed affected version ranges.
- Review endpoint controls for handling untrusted file attachments and downloads.
- Verify remediation against Adobe APSB21-55 guidance.
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
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CWE-125: Exact CWE lookup
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Open ATT&CK lookupCVE-2021-39858 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 (3.0)
- Known Exploited
- No
- Published
Vector: CVSS:3.0/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:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N1.81.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.0 score
3.3LowVector: CVSS:3.0/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/apsb21-55.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.