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CVE-2021-26567· NVD / CVE Program· CNA synology

Stack-based buffer overflow vulnerability in frontend/main.c in faad2 before 2.2.7.1 allow local attackers to execute arbitrary code via fil

Stack-based buffer overflow vulnerability in frontend/main.c in faad2 before 2.2.7.1 allow local attackers to execute arbitrary code via filename and pathname options.

HighCVSS 7.8 · v3.1—No exploit No fix recorded
Published
Feb 26, 2021
Updated
Jun 16, 2026
EPSS
1.1% · 65th percentile
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Report tools

JSON

Action score

31

Monitor

Low priority for now.

CVSS
31 / 40 · 7.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 1.1%

Affected systems

VendorProduct
synologydiskstation manager
synologyvs960hd firmware
synologyvs960hd
synologyskynas firmware
synologyskynas
synologydiskstation manager unified controller
synologyuc3200
faad2 projectfaad2

Affected versions

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

  • faad2 project faad2before 2.2.7.1
  • synology diskstation managerbefore 6.2.3-25426-3
  • synology diskstation manager unified controller3.0
  • synology skynas firmwareall versions
  • synology vs960hd firmwareall versions

Versions reported by the vendor

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

  • github/knik0 faad2

    • unspecified and later · before 2.2.7.1affected

Other highest-scoring records for the same primary product.

  • CVE-2013-6955webman/imageSelector.cgi in Synology DiskStation Manager (DSM) 4.0 before 4.0-2259, 4.2 before 4.2-3243, and 4.3 before 4.3-3810 Update 1 al
    65This week
  • CVE-2017-15889Command injection vulnerability in smart.cgi in Synology DiskStation Manager (DSM) before 5.2-5967-5 allows remote authenticated users to ex
    57Plan
  • CVE-2017-9554An information exposure vulnerability in forget_passwd.cgi in Synology DiskStation Manager (DSM) before 6.1.3-15152 allows remote attackers
    44Plan
  • CVE-2022-22687Buffer copy without checking size of input ('Classic Buffer Overflow') vulnerability in Authentication functionality in Synology DiskStation
    40Plan
  • CVE-2021-27649Use after free vulnerability in file transfer protocol component in Synology DiskStation Manager (DSM) before 6.2.3-25426-3 allows remote at
    40Plan
  • CVE-2021-27647Out-of-bounds Read vulnerability in iscsi_snapshot_comm_core in Synology DiskStation Manager (DSM) before 6.2.3-25426-3 allows remote attack
    40Plan

Remediation

Which version to upgrade to

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

No fix version is recorded for this entry. Check the references for vendor advisories.

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

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.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

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

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

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • 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
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

CVSS vector

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

nvd-primary

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.

Noroxi analysis

No Noroxi analysis for this record yet

We don't hand-write analysis for all 385,000+ vulnerabilities; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.

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Change log

No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.

References

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

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