I bypassed AWS API Gateway auth with a trailing slash. Got $12K bounty

https://theguptalog.blogspot.com/2026/04/i-bypassed-aws-api-gateway-auth-with.html

by tjek • 2 months ago

87 36 2 months ago

theguptalog.blogspot.com

A_Duck• 2 months ago

$1 removing the slash, $11,999 knowing where to remove the slash from

dizhn• 2 months ago

At that rate I would remove it from everywhere.

throw12345678912• 2 months ago

But do you know where they all are

redrove• 2 months ago

Don’t vibe code your auth path folks.

darkwater• 2 months ago

Otherwise a security research will vibe-code an exploit and slop out a blog post about it.

tedk-42• 2 months ago

Hmmm 12K seems like a bit much, even if it's fintech.

They also didn't mention the company.

The title feels clickbaity as it's not specific to AWS API gateway and instead, the implementation of it.

And who hosts on blogspot...

savolai• 2 months ago

It's not really fair to criticise hosting choice, but this lead me down a rabbit hole.

Noticed that non-responsive blog layouts are rare these days. Most are from blogspot. So I took a look and realized that blogger nowadays actually supports responsive layouts, but apparently... they are not popular?

https://blogger.googleblog.com/2017/03/share-your-unique-sty...

Kwpolska• 2 months ago

Google barely maintains Blogger, and people have old blogs with old templates they never felt the need to change.

Quarrelsome• 2 months ago

got any more criticisms, font choice, perhaps there's some duplication in their css?

I think 12k could be fine given how much it might have cost them if nobody had noticed.

rithdmc• 2 months ago

Or if someone with malicious intent noticed.

utf_8x• 2 months ago

Considering it let them do an unauthorized wire transfer from a system account, 12k seems pretty reasonable.

treszkai• 2 months ago

Yes, it and the other three posts sound positively AI written. The first post on the blog is how OP uploaded a backdoored dataset to HuggingFace and left it there for 6 months – whether made up or not, it doesn't sound great.

sillysaurusx3• 2 months ago

Why not?

This is arguing for style over substance. The goal is to explain how a bug impacts the company. Anything that achieves the goal is de facto good. Remember, the alternative is for the company not to be notified at all.

varispeed• 2 months ago

Exactly. What do these researchers think? Getting rich finding security flaws? They should get $5 at best, buy themselves chocolate bar and an orange juice and be grateful for the opportunity bestowed upon them by the rich.

paulryanrogers• 2 months ago

OJ here is over $5. Chocolate bars are not far behind. Of course I'm not complaining. Our kleptocrat overlords are doing great works!

mapcars• 2 months ago

Interesting story showing how complex todays tech is, and your whole security plan can be compromised by regexp matching rules.

sammy2255• 2 months ago

Did you Bypass AWS API Gateway.. or did you bypass it for a company who had their AWS API Gateway misconfigured?

stuartjohnson12• 2 months ago

I hate when people say this, as if there's any world in which I would want my AWS API gateway to do this, let alone accidentally. HTTP is littered with these footguns, differences between slashes and no slashes is a classic. A good piece of software would make it hard to do this by accident, and probably should default to having the same behaviour with or without trailing slash.

Yes yes, I know, folder/file naming convention dating from...

But it's current year now

sam_lowry_• 2 months ago

HTTP footguns? Meh! I routinely bypass domain blocks by appending a dot to the domain name, e.g. amazon.com.

fiedzia• 2 months ago

A good piece of software would make it hard to do this by accident, and probably should default to having the same behaviour with or without trailing slash.

Django redirects one version to another by default, which achieves that.

rvz• 2 months ago

The thing that absolutely should not be vibe coded, especially in fintech.

Turning a $10 bug into a $12K issue and if this was at a big tech company it would be a $120K+ issue.

brian_herman• 2 months ago

You deserve the trip, nice find!

praptak• 2 months ago

Appending stuff to bypass blacklists is eternal.

My first job, decades ago. I couldn't update something on my laptop because client's gateway blocked `http://foo.com/update.exe`. Guess what, `http://foo.com/update.exe?` worked as a bypass.

sillysaurusx3• 2 months ago

Ah, a rare situation where you have to put your URL in angle brackets for it to be parsed correctly here: <http://foo.com/update.exe?> (Not that it matters in this case. Also I would’ve guessed the angle brackets would disappear, but apparently not.)

[1] https://news.ycombinator.com/formatdoc

elpocko• 2 months ago

A DPI firewall at a place of education had a whitelist of allowed domains that you could connect to from the internal network. One entry in the whitelist was "microsoft.com".

I installed a web proxy on my VPS, which was accessible under a domain name like "computerthings.example", created a subdomain called "microsoft", and voila: "microsoft.computerthings.example" was good enough to match "^microsoft.com.*" and allowed us to bypass the block for the next two years.

anacrolix• 2 months ago

That's what you get for using Go mux

me551ah• 2 months ago

You didn’t break API Gateway or bypass it, you broke the company using incorrect api gateway config.

Your title is clickbait

Subdivide8452• 2 months ago

I want my 5 minutes back. What an absolute waste of time this was.

GeorgeWoff25• 2 months ago

The original article post https://vechron.com/2026/04/i-bypassed-aws-api-gateway-auth-...

localhoster• 2 months ago

Tbh I always wondered how are we still matching routes using regex and not something like a radix tree? That would eliminate these kinds of issues no?

flumpcakes• 2 months ago

This is a shocking mistake for a 'fintech' to make. This is supremely basic stuff.

I bypassed AWS API Gateway auth with a trailing slash. Got $12K bounty

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