How severe is CVE-2020-26521?

CVE-2020-26521 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2020-26521 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (79th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2020-26521?

CVE-2020-26521 primarily affects Linuxfoundation Nats-server. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2020-26521?

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

When was CVE-2020-26521 published?

CVE-2020-26521 was published on 2020-11-06 and last updated on 2026-06-17.

CVE-2020-26521

CVE-2020-26521 is a high-severity vulnerability in Linuxfoundation Nats-server with a CVSS 3.x base score of 7.5. 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-476.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 2% (79th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-476
Affected product: Linuxfoundation Nats-server
Published: 2020-11-06
Last modified: 2026-06-17

Description

The JWT library in NATS nats-server before 2.1.9 allows a denial of service (a nil dereference in Go code).

Frequently asked questions

What is CVE-2020-26521?: The JWT library in NATS nats-server before 2.1.9 allows a denial of service (a nil dereference in Go code).
How severe is CVE-2020-26521?: CVE-2020-26521 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2020-26521 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 2% (79th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2020-26521?: CVE-2020-26521 primarily affects Linuxfoundation Nats-server. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2020-26521?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2020-26521 published?: CVE-2020-26521 was published on 2020-11-06 and last updated on 2026-06-17.

References

Affected products (2)

cpe:2.3:a:linuxfoundation:nats-server:*:*:*:*:*:*:*:*
cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*

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CVE-2026-31657 — Critical (CVSS 9.8): In the Linux kernel, the following vulnerability has been resolved: batman-adv: hold claim backbone gateways by…
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