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CVE-2021-21373

20
FAUCET Score

CVE-2021-21373 affects Nimble, the package manager for the Nim programming language, in versions prior to 1.2.10 and 1.4.4. The vulnerability stems from Nimble's fallback mechanism, which retrieves package lists over unencrypted HTTP if the primary HTTPS connection fails. This medium-severity vulnerability (CVSS 5.9) allows a Man-in-the-Middle attacker to inject malicious package lists, leading to untrusted code execution if installed. There is no evidence of active exploitation, public exploit code, or significant community discussion surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
< 1.2.10CPE matchmatch criteria
cpe:2.3:a:nim-lang:nim:*:*:*:*:*:*:*:*
>= 1.4.0, < 1.4.4CPE matchmatch criteria
cpe:2.3:a:nim-lang:nim:*:*:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 3.1

7.5HIGH

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

Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
REQUIRED
Scope
CHANGED
Confidentiality Impact
LOW
Integrity Impact
HIGH
Availability Impact
LOW
Exploitability Score
1.6
Impact Score
5.3
CvssVersion
3.1

Exploit Intelligence

EPSS Score
1.16%
Probability of exploitation in next 30 days
EPSS Percentile
63.8%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0115 is in the 27th percentile among its peer group of 19,958 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.0 Bluesky, 0.0 Mastodon, and 0.2 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Remediation records are not available for this CVE.

References

consensys.net / diligence/vulnerabilities/nim-insecure-ssl-tls-defaults-remote-code-execution
ExploitThird Party Advisory
github.com / nim-lang/nimble/blob/master/changelog.markdown
Release NotesThird Party Advisory
github.com / nim-lang/security/security/advisories/GHSA-8w52-r35x-rgp8
Third Party Advisory