Security readout for executives and security teams
Plain-English summary
This vulnerability could let an attacker read sensitive memory from a user running affected Adobe Acrobat software, but only if the user opens a malicious file. It is not listed as CISA KEV in the supplied bundle, so prioritize patching exposed desktop fleets without treating it as confirmed active exploitation.
Executive priority
Address in normal vulnerability management cycles, with higher priority for teams handling external documents. Business urgency is moderate because user interaction is required and active exploitation is not evidenced here, but confidentiality impact is high.
Technical view
CVE-2021-39860 is a CWE-476 null pointer dereference in Adobe Acrobat Reader/Acrobat Pro DC search-related handling. CVSS 3.1 is 5.5: local attack vector, low complexity, no privileges, user interaction required, high confidentiality impact, no integrity or availability impact.
Likely exposure
Exposure is mainly endpoints with affected Adobe Acrobat Pro DC versions 2021.005.20060 and earlier, 2020.004.30006 and earlier, or 2017.011.30199 and earlier. The supplied affected-product data also names Acrobat Reader, but does not provide complete Reader version detail.
Exploitation context
The supplied sources say exploitation requires a victim to open a malicious file. They do not show CISA KEV listing or active exploitation evidence. Treat phishing and document-handling workflows as the practical risk path.
Researcher notes
Evidence is limited to the CVE data and Adobe advisory reference. The bundle does not provide exploit details, complete Reader version ranges, or independent exploitation confirmation. Avoid inferring affected builds beyond Adobe guidance.
Mitigation direction
- Check Adobe APSB21-55 for vendor-listed fixed versions and deployment guidance.
- Update affected Adobe Acrobat and Reader installations according to Adobe guidance.
- Prioritize users who regularly receive external PDF or document attachments.
- Restrict or sandbox handling of untrusted files where patching is delayed.
- Reinforce user reporting paths for suspicious document attachments.
Validation and detection
- Inventory Acrobat and Reader versions across managed endpoints.
- Compare installed builds against the affected version thresholds in the CVE bundle.
- Confirm update deployment succeeded on representative endpoints.
- Review email and endpoint telemetry for suspicious document delivery attempts.
- Verify no high-risk systems remain on unsupported Acrobat release tracks.
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-476: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-39860 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
- Medium
- CVSS
- 5.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/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:H/I:N/A:N1.83.6Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
5.5MediumVector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/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.
NULL Pointer Dereference
NULL Pointer Dereference represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.