What’s Vulnerable › Vulnerabilities

CVE-2021-21373: Nimble falls back to insecure http url when fetching packages

• Severity: medium (CVSS 5.9 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 1.2% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2021-03-26 · updated 2026-06-17
• Weakness: CWE-348

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.

Affected products

• nim-lang Nim: before 1.2.10; from 1.4.0 before 1.4.4 — fixed in 1.2.10, 1.4.4

How to fix

Upgrade to a fixed version: nim-lang Nim 1.2.10, 1.4.4. Check the vendor advisory for mitigations.

References

• https://consensys.net/diligence/vulnerabilities/nim-insecure-ssl-tls-defaults-remote-code-execution/
• https://github.com/nim-lang/nimble/blob/master/changelog.markdown#0130
• https://github.com/nim-lang/security/security/advisories/GHSA-8w52-r35x-rgp8
• https://consensys.net/diligence/vulnerabilities/nim-insecure-ssl-tls-defaults-remote-code-execution/
• https://github.com/nim-lang/nimble/blob/master/changelog.markdown#0130
• https://github.com/nim-lang/security/security/advisories/GHSA-8w52-r35x-rgp8

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