NVD / CVE Program· CNA adobe

CVE-2021-28550: Adobe Acrobat Reader use after free vulnerability could lead to arbitrary code execution

Noroxi assessment

Priority: Now (action score 81/100)

CISA has confirmed exploitation in the wild (Nov 3, 2021). Remediation deadline for US federal agencies: Nov 17, 2021.
Probability of exploitation in the next 30 days: 52.1% (FIRST EPSS); higher than 98.9% of all records.
Anyone who can reach it over the internet can trigger it. No account or password is required. A user must open a link or visit a page. No special conditions are required; it is repeatable.
Fixed version: tor (Alpine:v3.13) 0.4.4.9-r0; tor (Alpine:v3.14) 0.4.5.9-r0; tor (Alpine:v3.15) 0.4.6.5-r0.

Patch today or shut off access. Upgrade to tor (Alpine:v3.13) 0.4.4.9-r0; tor (Alpine:v3.14) 0.4.5.9-r0; tor (Alpine:v3.15) 0.4.6.5-r0 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · CISA KEV · FIRST EPSS

Acrobat Reader DC versions versions 2021.001.20150 (and earlier), 2020.001.30020 (and earlier) and 2017.011.30194 (and earlier) are affected by a Use After Free vulnerability. An unauthenticated attacker could leverage this vulnerability to achieve arbitrary code execution in the context of the current user. Exploitation of this issue requires user interaction in that a victim must open a malicious file.

HighCVSS 8.8 · v3.1KEVWeaponized Fix available

BDU:2021-02532

Published: Sep 2, 2021
Updated: Jun 16, 2026
EPSS: 52.1% · 98th percentile
CWE: CWE-416

Report tools

JSON

Action score

Now

Patch today or shut off access.

CVSS: 35 / 40 · 8.8 / 10
CISA KEV: 30 / 30 · Listed
EPSS: 16 / 30 · 52.1%

CISA SSVC decision

Exploitation: active
Automatable: no
Technical impact: total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD: 8.8
CNA · adobe: 9.6; 0.8 point gap

CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Actively exploited in the wild

CISA added this to its Known Exploited Vulnerabilities catalog on Nov 3, 2021. That signals real attacks, not theory.

Remediation deadline for US federal agencies: Nov 17, 2021.

Get told when this record changes

In CISA KEV: exploitation in the wild confirmed
Weaponized exploit exists
A fix has been released

If any of these changes, we'll tell you in the daily email digest.

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
adobe	acrobat dc	cpe:2.3:a:adobe:acrobat_dc
adobe	acrobat reader dc	cpe:2.3:a:adobe:acrobat_reader_dc
adobe	acrobat	cpe:2.3:a:adobe:acrobat
adobe	acrobat reader	cpe:2.3:a:adobe:acrobat_reader
microsoft	windows	cpe:2.3:o:microsoft:windows
apple	macos	cpe:2.3:o:apple:macos

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

adobe acrobat17.011.30059 and later · up to 17.011.30194 inclusive
adobe acrobat20.001.30005 and later · up to 20.001.30020 inclusive
adobe acrobat dc15.008.20082 and later · up to 21.001.20150 inclusive
adobe acrobat dc15.008.20082 and later · up to 21.001.20149 inclusive
adobe acrobat reader17.011.30059 and later · up to 17.011.30194 inclusive
adobe acrobat reader20.001.30005 and later · up to 20.001.30020 inclusive
adobe acrobat reader dc15.008.20082 and later · up to 21.001.20150 inclusive
adobe acrobat reader dc15.008.20082 and later · up to 21.001.20149 inclusive

Versions reported by the vendor

Affected version ranges reported by the assigning authority (adobe). Independent of NVD's CPE analysis and usually ahead of it.

Adobe Acrobat Reader
- unspecified and later · up to and including 2020.001.30020affected
- unspecified and later · up to and including 2021.001.20150affected
- unspecified and later · up to and including 2017.011.30194affected
- unspecified and later · up to and including Noneaffected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Alpine:v3.13	tor	before 0.4.4.9-r0	0.4.4.9-r0
Alpine:v3.14	tor	before 0.4.5.9-r0	0.4.5.9-r0
Alpine:v3.15	tor	before 0.4.6.5-r0	0.4.6.5-r0

Same product

adobe: all records

Other highest-scoring records for the same primary product.

CVE-2023-21608Adobe Acrobat Reader DC resetForm Use-After-Free Remote Code Execution VulnerabilityKEV
79This week
CVE-2018-4990Adobe Acrobat and Reader versions 2018.011.20038 and earlier, 2017.011.30079 and earlier, and 2015.006.30417 and earlier have a Double Free KEV
76This week
CVE-2020-9715Adobe Acrobat and Reader versions 2020.009.20074 and earlier, 2020.001.30002, 2017.011.30171 and earlier, and 2015.006.30523 and earlier havKEV
71This week

Published before and after this one in the same product

← EarlierCVE-2021-28631Aug 24, 2021 · Adobe Acrobat Reader DC AcroForm Field Use-After-Free Remote Code Execution Vulnerability
32Monitor
← EarlierCVE-2021-28632Aug 24, 2021 · ZDI-CAN-13471: Adobe Acrobat Reader DC AcroForm Field Use-After-Free Remote Code Execution Vulnerability
33Monitor
Later →CVE-2021-28553Sep 2, 2021 · Adobe Acrobat Reader use-after-free vulnerability could lead to arbitrary code execution
36Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
alpine:tor	0.4.4.9-r0 · Alpine:v3.13	Package registry (OSV)

Exploit status

Weaponized

A ready exploit tool or active in-the-wild use is known for this vulnerability. This should be your top priority.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

PublishedSep 2, 2021
CISA KEVNov 3, 2021+61 d
TodayNov 7, 2026+1891 d

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
A user must open a link or visit a page.
No special conditions are required; it is repeatable.

If successful

Confidentiality: high · data can be read
Integrity: high · data or configuration can be modified
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: Required
Scope: Unchanged
Confidentiality impact: High
Integrity impact: High
Availability impact: High

Weakness class (CWE)

CWE-416 · Use After Free

CVSS vector

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

nvd-primary

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

The bug in code

The whole CWE-416 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1free(dev->buf);
2/* ... another thread is still running ... */
3process(dev->buf);

Fixed

1lock(&dev->lock);
2free(dev->buf);
3dev->buf = NULL;
4unlock(&dev->lock);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

Fix✗ → ✓Nov 4, 2026, 3:41 AM UTC

For records you follow, these changes also arrive as notifications. →

References

helpx.adobe.com/security/products/acrobat/apsb21-29.html

Show all references (1 more)

www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-28550

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records