How severe is CVE-2021-21373?

CVE-2021-21373 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with high attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity high, and availability low.

Is CVE-2021-21373 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (63rd percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-21373?

CVE-2021-21373 affects Nim-lang Nim. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-21373?

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-2021-21373 published?

CVE-2021-21373 was published on 2021-03-26 and last updated on 2026-06-17.

CVE-2021-21373

CVE-2021-21373 is a high-severity vulnerability in Nim-lang Nim 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-295.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 4.3
EPSS exploit prediction: 1% (63rd percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-295
Affected product: Nim-lang Nim
Published: 2021-03-26
Last modified: 2026-06-17

Description

Nimble is a package manager for the Nim programming language. In Nim release versions before versions 1.2.10 and 1.4.4, "nimble refresh" fetches a list of Nimble packages over HTTPS by default. In case of error it falls back to a non-TLS URL http://irclogs.nim-lang.org/packages.json. An attacker able to perform MitM can deliver a modified package list containing malicious software packages. If the packages are installed and used the attack escalates to untrusted code execution.

Frequently asked questions

What is CVE-2021-21373?: Nimble is a package manager for the Nim programming language. In Nim release versions before versions 1.2.10 and 1.4.4, "nimble refresh" fetches a list of Nimble packages over HTTPS by default. In case of error it falls back to a non-TLS URL http://irclogs.nim-lang.org/packages.json. An attacker able to perform MitM can deliver a modified package list containing malicious software packages. If the packages are installed and used the attack escalates to untrusted code execution.
How severe is CVE-2021-21373?: CVE-2021-21373 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with high attack complexity, requires no privileges and user interaction. Impact on confidentiality is low, integrity high, and availability low.
Is CVE-2021-21373 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (63rd percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-21373?: CVE-2021-21373 affects Nim-lang Nim. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-21373?: 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-2021-21373 published?: CVE-2021-21373 was published on 2021-03-26 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:nim-lang:nim:*:*:*:*:*:*:*:*

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