CVE-2021-21373Public exploitNetwork attack vector

Code execution via HTTP package-list fallback

Published Mar 26, 2021 · Updated Aug 3, 2024

Improper source validation in Nimble before 1.2.10 and 1.4.0 through 1.4.3 allows man-in-the-middle attackers to supply a malicious package list. During nimble refresh, a failed HTTPS fetch causes the package-list downloader to retry a hard-coded HTTP endpoint without transport protection. Network interception must force the HTTPS request to fail; code execution occurs only if a delivered malicious package is subsequently installed and used.

CVSS severity7.5
High
EPSS probability1.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper source validation in Nimble before 1.2.10 and 1.4.0 through 1.4.3 allows man-in-the-middle attackers to supply a malicious package list. During nimble refresh, a failed HTTPS fetch causes the package-list downloader to retry a hard-coded HTTP endpoint without transport protection. Network interception must force the HTTPS request to fail; code execution occurs only if a delivered malicious package is subsequently installed and used.

The record

CVE
CVE-2021-21373
Published
Mar 26, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-348, CWE-295, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 26, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5GitHubCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:H/A:L
4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
5.9NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-348Use of Less Trusted Source
CWE-295Improper Certificate Validation
T1557Adversary-in-the-Middle

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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