CVE-2021-29495
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedNim is a statically typed compiled systems programming language. In Nim standard library before 1.4.2, httpClient SSL/TLS certificate verification was disabled by default. Users can upgrade to version 1.4.2 to receive a patch or, as a workaround, set "verifyMode = CVerifyPeer" as documented.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceIn Nim standard library before version 1.4.2, the httpClient module had SSL/TLS certificate verification disabled by default. This allowed man-in-the-middle attacks where attackers could intercept and modify encrypted traffic between the client and server, as certificate authenticity was never validated.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 1.4.2CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- High
- Availability
- None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check installed Nim versionRun 'nim --version' in your terminal and note the version numberAffected if The version is below 1.4.2 (e.g., 1.4.0, 1.2.0, etc.)
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Identify httpClient usage in your codebaseSearch your source files for 'import httpClient' or 'HttpClient' references using grep or your IDEAffected if You import and use the httpClient module in your project
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Check SSL verification configurationSearch your code for verifyMode settings. Look for patterns like 'newHttpClient()' followed by '.setSslConfig' or direct verifyMode assignments. Also check for 'verifyPeer = false' or 'SSLSocket' configurationsAffected if verifyMode is not set to CVerifyPeer, or SSL verification is explicitly disabled (verifyPeer = false), or no verifyMode is configured at all in code using Nim < 1.4.2
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Inspect SSL context setupIf you use custom SSL contexts, check for 'SslContext' or 'SSLSocket' usage and whether verifyMode is explicitly set to verify peersAffected if Custom SSL contexts do not set verifyMode = CVerifyPeer or similar peer verification settings
You are affected if you use Nim version below 1.4.2 AND use the httpClient module without explicitly setting verifyMode to validate certificates, as SSL/TLS verification was disabled by default in those versions.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor data1.4.2
Upgrade Nim to version 1.4.2 or later where certificate verification is enabled by default, or programmatically set verifyMode = CVerifyPeer in existing deployments as a workaround.
- Consultation2.0 h
- Implementation4.0 h
- Testing4.0 h
- Review / QA2.0 h
An estimate, not a bill — we confirm scope with you before any work starts. Need it this week? Rush from $3,328.
Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2021-29495 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2021-29495 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
- No weaponised exploit code, or anything meant to cause harm
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