Security readout for executives and security teams
Plain-English summary
This is a low-severity Adobe Acrobat Reader memory disclosure issue. A user must open a malicious PDF for exploitation. The likely business impact is limited on its own, but leaked memory could help an attacker bypass defenses such as ASLR during a broader attack chain.
Executive priority
Handle through routine desktop patching unless the organization has high exposure to untrusted PDFs or known outdated Reader deployments. This is not supported as an emergency issue by the provided evidence, but it should not remain unpatched because it can assist chained attacks.
Technical view
CVE-2021-40729 is a CWE-125 out-of-bounds read in Adobe Acrobat Reader DC affecting listed 21.x, 20.x, and 17.x builds and earlier. The CVSS 3.1 score is 3.3, with local attack vector, no privileges required, required user interaction, and low confidentiality impact only.
Likely exposure
Exposure is most likely on endpoints running Adobe Acrobat Reader DC 21.007.20095 or earlier, 21.007.20096 or earlier, 20.004.30015 or earlier, or 17.011.30202 or earlier. Systems where users open external PDFs have the most practical risk.
Exploitation context
The source bundle does not show CISA KEV listing or cited evidence of active exploitation. Exploitation requires convincing a victim to open a malicious PDF. The main concern is memory disclosure that may support mitigation bypass in a larger exploit chain.
Researcher notes
The provided data identifies the weakness class, affected Reader build ranges, user-interaction requirement, and ASLR-bypass relevance. It does not provide exploit details, observed exploitation, or fixed version numbers in the bundle. Use Adobe APSB21-104 as the authoritative remediation reference.
Mitigation direction
- Review Adobe APSB21-104 for the vendor-approved fixed Reader versions.
- Update affected Acrobat Reader installations through normal patch management.
- Prioritize endpoints that handle external or untrusted PDF files.
- Maintain user controls against opening unexpected PDF attachments or links.
- Remove unsupported Reader versions where upgrade is not possible.
Validation and detection
- Inventory Adobe Acrobat Reader versions across managed endpoints.
- Compare installed builds against the affected version thresholds in the CVE record.
- Confirm patch management references Adobe APSB21-104 or later fixed guidance.
- Check whether exposed user groups routinely receive untrusted PDFs.
- Document any remaining legacy Reader installations and compensating controls.
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
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-2021-40729 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/apsb21-104.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.