LiveActive security incident?Get immediate response
CVE Record

CVE-2021-21057: Acrobat Reader DC Invalid Memory Read Due To An Uninitialized Pointer

Acrobat Reader DC versions versions 2020.013.20074 (and earlier), 2020.001.30018 (and earlier) and 2017.011.30188 (and earlier) are affected by a null pointer dereference vulnerability when parsing a specially crafted PDF file. An unauthenticated attacker could leverage this vulnerability to achieve denial of service in the context of the current user. Exploitation of this issue requires user interaction in that a victim must open a malicious file.

MediumCVSS 6.6Not KEV-listedUpdated
Discuss exposureBack to CVEs
Glexia's TakeAutomated analysismoderate

Security readout for executives and security teams

Plain-English summary

This flaw can crash Adobe Acrobat Reader DC when a user opens a malicious PDF. It requires user interaction, but no attacker login is needed. Business impact is mainly disruption on affected endpoints, with limited confidentiality and integrity impact reflected in the CVSS vector.

Executive priority

Treat as a moderate endpoint hygiene issue. Patch through normal Adobe update processes, prioritizing users who frequently receive external PDFs.

Technical view

CVE-2021-21057 is a CWE-476 null pointer dereference in Acrobat Reader DC PDF parsing. A specially crafted PDF can trigger denial of service in the current user's context. The CVSS 3.1 score is 6.6, with local attack vector, low complexity, no privileges, and required user interaction.

Likely exposure

Exposure is limited to environments running Acrobat Reader DC 2020.013.20074 and earlier, 2020.001.30018 and earlier, or 2017.011.30188 and earlier.

Exploitation context

The source bundle does not identify active exploitation, and CISA KEV is false. Exploitation requires a victim to open a malicious PDF file. Sources do not provide public exploit maturity details.

Researcher notes

Evidence supports denial of service from malformed PDF parsing, not remote code execution. The bundle names null pointer dereference and uninitialized pointer wording, but does not include detailed root-cause analysis or fixed build numbers.

Mitigation direction

  • Review Adobe APSB21-09 for the vendor-designated fixed versions and update guidance.
  • Prioritize updating affected Acrobat Reader DC installations on user workstations.
  • Warn users not to open unexpected or untrusted PDF files.
  • Confirm endpoint software inventory captures Acrobat Reader DC version branches.

Validation and detection

  • Inventory Acrobat Reader DC versions across managed endpoints.
  • Compare installed versions against the affected version thresholds in the CVE description.
  • Confirm update deployment status against Adobe APSB21-09 guidance.
  • Review helpdesk or endpoint telemetry for PDF-triggered Reader crashes.
Prepared
Confidence
high
Sources
3

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

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 · low confidence lookup

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 lookup
cve · low confidence lookup

CVE-2021-21057 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
Medium
CVSS
6.6 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H

Official CVE source material

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.

1CVSS vectors
0Timeline events
0ADP providers
2Source links

CVSS vector scores

1 official score

We 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.

ScoreVersionSeverityVectorExploitImpactSource
6.6CVSS 3.1MediumCVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H1.84.7Primary CVE score

Vulnerability scoring details

Base CVSS 3.1 score

6.6Medium
CVSS 3.1 vector shape for CVE-2021-21057Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:H

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
AdobeAcrobat Readerunspecified, unspecified, unspecified, unspecifiedListed
Weakness

CWE details

CWE-476

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-476 · source CWE mapping

NULL Pointer Dereference

NULL Pointer Dereference represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs