Error attempting to repeat a file from an S3 bucket: Potential MFA bug.
It is a very unhelpful error message, isn’t it?
Repair: Align the error message with the precise repair the person must make.
There are two sides to S3 permissions. One is the permission to take S3 actions in any respect which is outlined within the IAM Permissions for the person, a bunch the person is in, or a task the person has assumed. Navigate to IAM, click on on insurance policies on the left, after which create a coverage that grants S3 permissions. Assign that to the person, group or function that may’t entry the S3 bucket.
The second aspect is permission by way of the S3 bucket coverage. By default it’s best to have entry to a bucket by way of the bucket coverage in your individual account. Nonetheless, in order for you cross-account entry you’ll want so as to add that permission to your bucket coverage.
In my case, I used to be attempting to provide a person entry to any bucket in a specific OU.
It doesn’t appear to be working as of but. Once I observe the above directions, AWS IAM says the coverage grants no permissions. The issue was that I forgot the * within the coverage beneath:
"ForAnyValue:StringLike": {
"aws:PrincipalOrgPaths": "[org-id]/[root-id]/[ou-id]/*"
}
Tip: Get the group id, root id, and OU ID from the AWS console on the organizations web page or question it utilizing the AWS CLI.
Even after addressing that drawback I nonetheless couldn’t entry the bucket. I had another doable points however to resolve the issue I merely granted full learn entry to s3 in my IAM Coverage. Then I used to be capable of obtain the file. After all that’s not what I need however that is what folks do when error messages should not useful.
Repair: On this case neither the S3 error message nor the IAM error message are very helpful. It looks as if AWS may tackle the truth that I would like a /* right here. The identical is true for related issues in S3 bucket insurance policies the place some instructions require a /* on the finish of the bucket identify and different instructions apply on to the bucket. Moreover, some actions require pre-requisite actions. Assist a person out and supply extra info.
Then I navigated to my function and click on on the IAM entry analyzer tab. Right here ai can see that AWS S3 was referred to as. However which motion?
I click on on Amazon S3 and I solely see one motion despite the fact that I downloaded a file from one other account:
So it seems right here that the cross-account entry isn’t coated by the IAM Entry Analyzer.
FIX: This tab wants to point out cross account entry and permissions utilized in that case. There needs to be a GetObject operation right here.
Since this function doesn’t exist within the different account I can’t use the AWS IAM entry analyzer over there. I can test CloudTrail logs. Nonetheless, in CloudTrail I can solely see the AssumeRole motion.
With a view to see the S3 actions you need to activate S3 Information Occasions — one thing that was important within the Capital One Breach aftermath and a subject I cowl in my cloud safety courses. After all, that may price you more money.
So to get this working I each disabled the organizational restriction and the MFA requirement. Attempt including each of them one after the other and see which one causes failure, in the event that they do.
Aha. Imposing MFA on this request causes the bucket entry to fail — despite the fact that I’m authenticated with MFA.
Repair: This looks as if a bug. This could work with assume function utilizing MFA and MFA required within the IAM coverage to name the S3 instructions.
Let’s take away the situation that requires MFA and add the organizational unit. That fails as properly. The factor is that the account making the request within the OU. The restriction to the OU is perhaps on the caller being within the designated OU relatively than permitting entry to assets within the OU. Nicely, I’m undecided but it surely doesn’t work both.
Do any circumstances work? Let’s attempt IP tackle.
I take away all circumstances and as soon as once more, I can entry my file.
Nope. That causes the identical error. So it seems that with cross-account entry you can not put any situation in your IAM Coverage that’s used for cross-account entry.
BUGOr incomplete implementation. This could work.When groups take a look at options there needs to be a regular record of take a look at instances that they undergo to confirm all doable paths work appropriately. One thing does not work right here or on the very least the error message must be extra particular.Additionally any documentation associated to circumstances, OU useful resource entry, and so forth. ought to clearly name out any limitations or identified points.Code ought to tackle frequent misconfigurations comparable to a lacking * and ask the person in the event that they meant one thing totally different which may work (so long as it doesn't introduce safety issues.)NOTE: There may be one potential difficulty and that may be a lag within the time from which you implement an IAM coverage and it truly takes impact. The AWS IAM console and CLI ought to actually have a solution to confirm that the function is, in actual fact, in impact in any other case testing is an excessive amount of of a guessing sport resulting from eventual consistency points.
OK shifting on for the second…will revisit this later to see if it will get fastened.
So I already talked about above that my try at granting entry to a whole OU may not work for numerous causes. Nonetheless, I examined this in opposition to a bucket in the identical account and found out that the MFA required to imagine the function doesn’t present up within the request made by the function after that time. Meaning you may’t implement MFA in circumstances with assume function if I perceive appropriately. I believe it could be a good suggestion to vary this habits so you might use MFA circumstances the way in which I’m attempting to do above.
Right here’s a associated difficulty with PutObject for a neighborhood account S3 bucket.
Teri Radichel — Comply with me @teriradichel on Twitter
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