How severe is CVE-2021-26562?

CVE-2021-26562 has a CVSS 3.x base score of 9.0, rated critical severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2021-26562 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (75th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-26562?

CVE-2021-26562 primarily affects Synology Diskstation Manager. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-26562?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2021-26562 published?

CVE-2021-26562 was published on 2021-02-26 and last updated on 2026-06-17.

CVE-2021-26562

CVE-2021-26562 is a critical-severity vulnerability in Synology Diskstation Manager with a CVSS 3.x base score of 9.0. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-787.

Key facts

Severity: Critical (CVSS 3.x base score 9.0)
CVSS v2: 6.8
EPSS exploit prediction: 2% (75th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-787
Affected product: Synology Diskstation Manager
Published: 2021-02-26
Last modified: 2026-06-17

Description

Out-of-bounds write vulnerability in synoagentregisterd in Synology DiskStation Manager (DSM) before 6.2.3-25426-3 allows man-in-the-middle attackers to execute arbitrary code via syno_finder_site HTTP header.

Frequently asked questions

What is CVE-2021-26562?: Out-of-bounds write vulnerability in synoagentregisterd in Synology DiskStation Manager (DSM) before 6.2.3-25426-3 allows man-in-the-middle attackers to execute arbitrary code via syno_finder_site HTTP header.
How severe is CVE-2021-26562?: CVE-2021-26562 has a CVSS 3.x base score of 9.0, rated critical severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-26562 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (75th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-26562?: CVE-2021-26562 primarily affects Synology Diskstation Manager. In total, 4 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-26562?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-26562 published?: CVE-2021-26562 was published on 2021-02-26 and last updated on 2026-06-17.

References

Affected products (4)

cpe:2.3:o:synology:diskstation_manager:*:*:*:*:*:*:*:*
cpe:2.3:o:synology:vs960hd_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:synology:skynas_firmware:-:*:*:*:*:*:*:*
cpe:2.3:o:synology:diskstation_manager_unified_controller:3.0:*:*:*:*:*:*:*

More vulnerabilities in Synology Diskstation Manager

CVE-2022-27626 — Critical (CVSS 10.0): A vulnerability regarding concurrent execution using shared resource with improper synchronization ('Race Condition')…
CVE-2022-27625 — Critical (CVSS 10.0): A vulnerability regarding improper restriction of operations within the bounds of a memory buffer is found in the…
CVE-2022-27624 — Critical (CVSS 10.0): A vulnerability regarding improper restriction of operations within the bounds of a memory buffer is found in the…
CVE-2013-6955 — Critical (CVSS 10.0): webman/imageSelector.cgi in Synology DiskStation Manager (DSM) 4.0 before 4.0-2259, 4.2 before 4.2-3243, and 4.3 before…
CVE-2024-10441 — Critical (CVSS 9.8): Improper encoding or escaping of output vulnerability in the system plugin daemon in Synology BeeStation OS (BSM)…
CVE-2022-22687 — Critical (CVSS 9.8): Buffer copy without checking size of input ('Classic Buffer Overflow') vulnerability in Authentication functionality in…

All CVEs affecting Synology Diskstation Manager →

Other CWE-787 (Out-of-bounds Write) vulnerabilities

CVE-2026-42369 — Critical (CVSS 10.0): GV-VMS V20 is a Video Monitoring Software used to gather the feeds of many surveillance cameras and manage other…
CVE-2026-4746 — Critical (CVSS 10.0): Out-of-bounds Write vulnerability in timeplus-io proton (base/poco/Foundation/src‎ modules). This vulnerability is…
CVE-2025-43300 — Critical (CVSS 10.0): An out-of-bounds write issue was addressed with improved bounds checking. This issue is fixed in iOS 15.8.5 and iPadOS…
CVE-2025-24201 — Critical (CVSS 10.0): An out-of-bounds write issue was addressed with improved checks to prevent unauthorized actions. This issue is fixed in…
CVE-2024-42479 — Critical (CVSS 10.0): llama.cpp provides LLM inference in C/C++. The unsafe `data` pointer member in the `rpc_tensor` structure can cause…
CVE-2024-39791 — Critical (CVSS 10.0): Stack-based buffer overflow vulnerabilities affecting Vonets industrial wifi bridge relays and wifi bridge…

Browse all CWE-787 (Out-of-bounds Write) vulnerabilities →