# CVE-2020-8918: TPM 1.2 key authorization values are vulnerable to a TPM transport eavesdropper

> An eavesdropper can recover TPM key authorization values due to improper initialization in the go-tpm library, exposing sensitive credentials.

- **Severity:** Medium 6.3 (`CVSS:3.1/AV:L/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 11 Aug 2020
- **Updated:** 4 Aug 2024
- **Also known as:** GHSA-5x29-3hr9-6wpw, GO-2021-0095

## What is CVE-2020-8918?

CVE-2020-8918 is a medium-severity vulnerability in google/go-tpm library, published on 11 Aug 2020. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.

### Official description

An improperly initialized 'migrationAuth' value in Google's go-tpm TPM1.2 library versions prior to 0.3.0 can lead an eavesdropping attacker to discover the auth value for a key created with CreateWrapKey. An attacker listening in on the channel can collect both 'encUsageAuth' and 'encMigrationAuth', and then can calculate 'usageAuth ^ encMigrationAuth' as the 'migrationAuth' can be guessed for all keys created with CreateWrapKey. TPM2.0 is not impacted by this. We recommend updating your library to 0.3.0 or later, or, if you cannot update, to call CreateWrapKey with a random 20-byte value for 'migrationAuth'.

Weakness: CWE-665 (Improper Initialization)

## Which versions are affected by CVE-2020-8918?

3 open source packages ship an affected version, including github.com/google/go-tpm. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `github.com/google/go-tpm` | Go | All versions | 0.3.0 |
| `github.com/google/go-tpm` | Go | All versions | 0.3.0 |
| `github.com/google/go-tpm` | Go | All versions | 0.3.0 |

Products: Google Go-Tpm.

## How do I fix CVE-2020-8918?

Upgrade github.com/google/go-tpm to 0.3.0 or later.

## Is CVE-2020-8918 being exploited?

There is no known exploitation of CVE-2020-8918 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2020-8918 and fix it if it is affected.

What it is: CVE-2020-8918 is a medium-severity vulnerability in google/go-tpm library, published on 11 Aug 2020. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2020-8918 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/google/go-tpm (Go): affected all versions; fixed in 0.3.0
- github.com/google/go-tpm (Go): affected all versions; fixed in 0.3.0
- github.com/google/go-tpm (Go): affected all versions; fixed in 0.3.0

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2020-8918/ (Markdown: https://insights.sbomify.com/CVE-2020-8918/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2020-8918
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2020-8918
- OSV: https://osv.dev/vulnerability/CVE-2020-8918

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From sbomify Insights: https://insights.sbomify.com/CVE-2020-8918/
Summaries are generated and may contain mistakes; the official description above is the record.