Cybersecurity · head to head
Cosign vs Microsoft Defender
Cosign
Cybersecurity
Signs and verifies container images and artifacts, with or without managing keys
- From
- Free
- Rated
- -
Microsoft Defender
Cybersecurity
Always-on protection for you and your family's data and devices
- From
- $12/month
- Rated
- -
The short version
- Only Cosign has a free tier, so it costs nothing to try first.
- Each has a real cost: Cosign keyless signing inherits every weakness of the identity provider behind it. Sigstore’s own threat model states that if an identity provider is compromised, Sigstore will issue certificates to those identities, so a compromised account produces perfectly valid signatures.; Microsoft Defender defender Suite requires existing Microsoft 365 E3 or equivalent base licensing
- Prices and features above were last checked on 31 August 2026.
Where they differ
Only the attributes on which Cosign and Microsoft Defender actually diverge.
| Attribute | Cosign | Microsoft Defender |
|---|---|---|
| Starting price | Free | $12/month |
| Pricing model | Open source, no licence fee | subscription |
| Free tier | Yes | No |
| Platforms | macOS, Linux, Windows, Docker | Web |
Identical on both: user rating (Not yet rated), category (Cybersecurity).
What each one covers
Drawn from each product's published feature list. An absence here means we hold no record of it - not that the product lacks it.
Only in Cosign
- Keyless signing
- Key and KMS signing
- Registry-native storage
- In-toto attestations
- Offline verification
- Trusted root and signing config
Only in Microsoft Defender
Nothing recorded that Cosign does not also cover.
What people use each for
The jobs each tool is most often brought in to do.
Cosign
- Signing container images in a build pipeline without managing long-lived private keysnot Microsoft Defender
- Attaching a signed bill of materials to a release so consumers can verify its provenancenot Microsoft Defender
- Meeting a customer or regulatory requirement for signed artifactsnot Microsoft Defender
- Verifying third-party images before they enter an internal registrynot Microsoft Defender
Microsoft Defender
- Endpoint security and threat protectionnot Cosign
- Identity and access securitynot Cosign
- Email threat protectionnot Cosign
- SaaS application security monitoringnot Cosign
Where each one falls short
Documented limitations, not opinions. Every one is a constraint you would hit in normal use.
Cosign
- Keyless signing inherits every weakness of the identity provider behind it. Sigstore’s own threat model states that if an identity provider is compromised, Sigstore will issue certificates to those identities, so a compromised account produces perfectly valid signatures.
- A signature proves who signed, never whether they should have. The documentation is explicit that Sigstore cannot determine authorisation, so every consumer must write and maintain their own identity and issuer policy or verification means nothing.
- Nothing is enforced without an admission controller. Signing changes what you can prove, not what runs, and the official policy controller has a small maintainer base for a component sitting in a cluster admission path.
- Upgrades break pipelines. Version 3 changed defaults, version 4 is announced as removing legacy functionality and roughly half the command line flags, and two official client libraries still lacked support for the new log format as of mid 2026.
- Signatures do not expire. An artifact signed before a maintainer account was compromised and one signed after are indistinguishable unless somebody is actively monitoring the transparency log, and almost nobody is.
Microsoft Defender
- Defender Suite requires existing Microsoft 365 E3 or equivalent base licensing
- Some Defender products use pay-as-you-go pricing with variable costs
- Prices vary based on Microsoft agreements, requiring sales contact for custom quotes
Pricing, plan by plan
Cosign
Free- CosignFree
- Apache-2.0
- Public Sigstore infrastructure free to use
- No usage limits published
Microsoft Defender
$12/month- Microsoft Defender Suite$12/month
- Endpoint protection
- Identity threat detection
- Email security
- Microsoft 365 E5 with Defender$60/month
- Includes Defender Suite
- Microsoft Teams included
- Comprehensive security and compliance
- Microsoft Defender Vulnerability Management Add-on$2/month
- Vulnerability scanning and management
- One-month free trial available
- Annual commitment required
Which should you pick?
Choose Cosign if
- You need keyless signing.
- You want to start without paying.
- You work on macOS, Linux, Windows, Docker.
- You also want key and kms signing.
Choose Microsoft Defender if
Nothing in the data separates Microsoft Defender from Cosign on the points above - pick on price and on how each one feels to use.
Questions people ask
- Is Cosign or Microsoft Defender better?
- Neither clearly leads. Cosign starts at Free and Microsoft Defender at $12/month, and user ratings are close enough to be indistinguishable. Choose on capability and platform support.
- Which is cheaper, Cosign or Microsoft Defender?
- Cosign has a free tier; the other does not. Paid plans start at Free for Cosign and $12/month for Microsoft Defender.
- Does Cosign or Microsoft Defender run on more platforms?
- Cosign runs on macOS, Linux, Windows, Docker. Microsoft Defender runs on Web.
- Can I use Cosign for free?
- Yes. Cosign has a free tier, so you can try it without paying. Microsoft Defender starts at $12/month.
- What is Cosign best used for?
- Cosign is most often used for signing container images in a build pipeline without managing long-lived private keys, attaching a signed bill of materials to a release so consumers can verify its provenance, meeting a customer or regulatory requirement for signed artifacts, verifying third-party images before they enter an internal registry. Of those, signing container images in a build pipeline without managing long-lived private keys and attaching a signed bill of materials to a release so consumers can verify its provenance are not what Microsoft Defender is typically brought in for.
- What can Cosign do that Microsoft Defender cannot?
- Cosign covers Keyless signing, Key and KMS signing, Registry-native storage, In-toto attestations.
Answered from the vendors’ own pages
Cosign: Does Cosign tell me if an image is vulnerable?
No. It has no vulnerability knowledge whatsoever. It can carry an SBOM as a signed attestation but never reads it. Pair it with a scanner.
Microsoft Defender: How much does Microsoft Defender Suite cost?
Microsoft Defender Suite costs $12/user/month (paid yearly), but requires existing Microsoft 365 E3 or equivalent base licensing. It includes endpoint protection, identity threat detection, email security, and SaaS application monitoring.
SourceCosign: Is signing alone enough?
No. Verification is a command somebody runs. Without an admission controller enforcing it, an unsigned image still runs.
Microsoft Defender: What add-ons are available for Microsoft Defender?
Microsoft Defender Vulnerability Management Add-on costs $2/user/month with annual commitment and includes a one-month free trial. Additional pay-as-you-go products include External Attack Surface Management, Cloud Security Posture Management, and Sentinel.
SourceCosign: What does a bare cosign verify actually prove?
Very little. Without a pinned certificate identity and OIDC issuer, it accepts a valid signature from any identity at all.
Microsoft Defender: Is Defender included in Microsoft 365 E5?
Yes, Microsoft Defender Suite is included in Microsoft 365 E5 at $60/user/month (paid yearly with Teams). Prices may vary based on Microsoft agreements, requiring contact with Sales for customized quotes.
SourceCosign: What is the risk of keyless signing?
Your OIDC provider becomes the root of trust. Compromise of that account yields genuine, verifiable signatures, so account security is the control that matters.
Cosign: Should we expect breaking changes?
Yes. Version 4 is announced to remove roughly half the flags, and a post-quantum migration is named as a further breaking change after that.
Related pages
More on Microsoft Defender
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