Security readout for executives and security teams
Plain-English summary
This vulnerability can let a malicious PDF leak some system information from a user who opens it in vulnerable Adobe Acrobat Reader versions. It is not described as actively exploited in the provided sources, and it requires user interaction, so urgency is moderate rather than emergency-level.
Executive priority
Treat this as a routine but time-bounded desktop patching item. It can expose information but needs user interaction and has no confirmed active exploitation in the supplied evidence.
Technical view
CVE-2021-28557 is a CWE-125 out-of-bounds read in PDFLibTool affecting Acrobat Reader DC 2021.001.20150 and earlier, 2020.001.30020 and earlier, and 2017.011.30194 and earlier. Impact is limited to low confidentiality exposure in the current user context.
Likely exposure
Exposure is most likely on endpoints running the listed Acrobat Reader DC versions or earlier, especially where users routinely open external PDF attachments or downloads.
Exploitation context
The sources say exploitation requires a victim to open a malicious file. The CVE is not listed as KEV in the supplied bundle, so active exploitation is not established here.
Researcher notes
The provided evidence does not include exploit details, observed attacks, or explicit fixed build numbers. Focus validation on version exposure, Adobe advisory mapping, endpoint coverage, and PDF ingress controls.
Mitigation direction
- Update Acrobat Reader according to Adobe APSB21-29 guidance.
- Prioritize endpoints with external email or web-downloaded PDF exposure.
- Remove vulnerable Acrobat Reader installations where not required.
- Use mail and web controls to reduce malicious PDF delivery.
- Check Adobe guidance for any additional vendor-supported mitigations.
Validation and detection
- Inventory installed Acrobat Reader versions across managed endpoints.
- Compare versions against 2021.001.20150, 2020.001.30020, and 2017.011.30194 thresholds.
- Confirm updates were applied after remediation.
- Review security telemetry for suspicious PDF activity, without assuming compromise.
- Validate user-facing PDF handling controls for high-risk groups.
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-2021-28557 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
- 4.3 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/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:N/AC:L/PR:N/UI:R/S:U/C:L/I:N/A:N2.81.4Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
4.3MediumVector: CVSS:3.1/AV:N/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/apsb21-29.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.