FIXED : Conflicted , Repeated Transaction in QT

[EthanB]

Initially I had contacted : https://bitcointalk.org/index.php?action=profile;u=554646 for a Panera Gift-Card : https://bitcointalk.org/index.php?topic=1198141.0

I had agreed to send him BTC, and once I did I appeared to have an issue with the transaction.


Status: 2/unconfirmed
Date: 10/4/2015 20:44
To: 12rArQuEJJGbn2MQUM9QwBh7gFPami4ck2
Debit: -0.03000000 BTC
Transaction fee: -0.00000918 BTC
Net amount: -0.03000918 BTC
Transaction ID: 4480c906a09ea358a2b5c0345af646f8b9a544043b870d787d37a8fcafcd470b-000


This is the original transaction I sent to the user from Bitcoin Core. Then later, I got another transaction notification come through...

Status: conflicted, broadcast through 14 nodes
Date: 10/4/2015 20:44
To: 12rArQuEJJGbn2MQUM9QwBh7gFPami4ck2
Debit: -0.03000000 BTC
Transaction fee: -0.00000918 BTC
Net amount: -0.03000918 BTC
Transaction ID: 4d0a0f91a4f09e0ae7c24bc60f2438d9f741b271182fbec433144fa332a784c9-000

I did not send this myself, and I am confused to what is happening. Help?

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[achow101]

Someone was doing transaction malleability attacks (thread here: https://bitcointalk.org/index.php?topic=1198032.0). This confuses most clients since the transaction ids are different. The two transactions appear as double spends. Don't worry, your bitcoin is safe. Transaction malleability only changes the txid, not the actual inputs and outputs, so your bitcoin is going to wherever you intended it to go originally. Just don't spend any Bitcoin from either of those transactions because only one will be confirmed and you don't know which one.

[EthanB]

Someone was doing transaction malleability attacks (thread here: https://bitcointalk.org/index.php?topic=1198032.0). This confuses most clients since the transaction ids are different. The two transactions appear as double spends. Don't worry, your bitcoin is safe. Transaction malleability only changes the txid, not the actual inputs and outputs, so your bitcoin is going to wherever you intended it to go originally. Just don't spend any Bitcoin from either of those transactions because only one will be confirmed and you don't know which one.

EDIT : Reading through the thread and I see it's a bigger scare than anything.. Not a serious threat if waiting for confirmations.

[achow101]

Someone was doing transaction malleability attacks (thread here: https://bitcointalk.org/index.php?topic=1198032.0). This confuses most clients since the transaction ids are different. The two transactions appear as double spends. Don't worry, your bitcoin is safe. Transaction malleability only changes the txid, not the actual inputs and outputs, so your bitcoin is going to wherever you intended it to go originally. Just don't spend any Bitcoin from either of those transactions because only one will be confirmed and you don't know which one.

I have only ever sent BTC from this wallet to that one specific user, does this mean he specifically targeted me to perform this attack?
How can I prevent this from happening?
What would happen if he was successful, and how to prevent that?

No, anyone can perform a transaction malleability attack. Anyone can retrieve your transaction and modify it in such a way that the txid changes but not the inputs or outputs.

There is no way to prevent this kind of attack. The wallet should automatically clear itself up once one of the transactions becomes confirmed. To protect yourself, don't send any Bitcoin from any unconfirmed transaction (general rule of thumb anyways).

[EthanB]

Someone was doing transaction malleability attacks (thread here: https://bitcointalk.org/index.php?topic=1198032.0). This confuses most clients since the transaction ids are different. The two transactions appear as double spends. Don't worry, your bitcoin is safe. Transaction malleability only changes the txid, not the actual inputs and outputs, so your bitcoin is going to wherever you intended it to go originally. Just don't spend any Bitcoin from either of those transactions because only one will be confirmed and you don't know which one.

I have only ever sent BTC from this wallet to that one specific user, does this mean he specifically targeted me to perform this attack?
How can I prevent this from happening?
What would happen if he was successful, and how to prevent that?

No, anyone can perform a transaction malleability attack. Anyone can retrieve your transaction and modify it in such a way that the txid changes but not the inputs or outputs.

There is no way to prevent this kind of attack. The wallet should automatically clear itself up once one of the transactions becomes confirmed. To protect yourself, don't send any Bitcoin from any unconfirmed transaction (general rule of thumb anyways).

So it's just an attack on the bitcoin network to exploit a redundant and insignificant "security" flaw?
Meaning, there's no benefit or negative other than weird looking transactions temporarily?

[achow101]

So it's just an attack on the bitcoin network to exploit a redundant and insignificant "security" flaw?
Meaning, there's no benefit or negative other than weird looking transactions temporarily?

Pretty much.

Although with any poorly written code, it can completely screw with it and in some cases, websites can be tricked that a transaction didn't happen. A scenario would be something like a website that you can withdraw bitcoin from is only checking one particular txid for the withdraw, not the balance of the address. Then if the withdraw transaction is mutated and then confirmed and the original is dropped from the mempool, the website thinks that the withdraw didn't go through and in their database it is canceled. In reality, the withdraw did happen, but the site thinks it didn't so the user can still withdraw the same amount. This is an extremely unlikely scenario, but it could happen with bad code.

[EthanB]

So it's just an attack on the bitcoin network to exploit a redundant and insignificant "security" flaw?
Meaning, there's no benefit or negative other than weird looking transactions temporarily?

Pretty much.

Although with any poorly written code, it can completely screw with it and in some cases, websites can be tricked that a transaction didn't happen. A scenario would be something like a website that you can withdraw bitcoin from is only checking one particular txid for the withdraw, not the balance of the address. Then if the withdraw transaction is mutated and then confirmed and the original is dropped from the mempool, the website thinks that the withdraw didn't go through and in their database it is canceled. In reality, the withdraw did happen, but the site thinks it didn't so the user can still withdraw the same amount. This is an extremely unlikely scenario, but it could happen with bad code.

Ahhh, thanks for the clarification; That helps my understanding tremendously.
Although it could help improve a-lot of software, before bitcoin gets even more valuable.

[mihtju]

I have the same issue and my balance now is in -
So what should I do, will be second transaction be returned to me after some time? Or I need to contact blockchain?

My wallet: 1HkLh2rY3xrPD6frVit7ANvtjmmaiKrgFP

[shorena]

I have the same issue and my balance now is in -
So what should I do, will be second transaction be returned to me after some time? Or I need to contact blockchain?

My wallet: 1HkLh2rY3xrPD6frVit7ANvtjmmaiKrgFP

You dont have the same issue if you can "contact blockchain". OP is running a full node you are using a service. Contact support.

@EthanB is the conflicted TX removed from your wallet or is it still showing? If its still showing you can remove it by starting core with -zapwallettxes e.g. on Windows, close core, make sure its closed, hit Win + R (to start "run") enter

Code:

C:\Program Files (x86)\Bitcoin\bitcoin-qt.exe -zapwallettxes

you might have to change this slightly depending where you installed core. Once you did this, just click ok and core will start rescanning all known blocks for your transactions. This can take a few minutes depending on your CPU and disk speed. Afterwards the conflicting TX should be gone and your wallet back to normal.

[Dave Wilkinson]

just wait it out, time usually fixes everything with the blockchain.

[EthanB]

I have the same issue and my balance now is in -
So what should I do, will be second transaction be returned to me after some time? Or I need to contact blockchain?

My wallet: 1HkLh2rY3xrPD6frVit7ANvtjmmaiKrgFP

You dont have the same issue if you can "contact blockchain". OP is running a full node you are using a service. Contact support.

@EthanB is the conflicted TX removed from your wallet or is it still showing? If its still showing you can remove it by starting core with -zapwallettxes e.g. on Windows, close core, make sure its closed, hit Win + R (to start "run") enter

Code:

C:\Program Files (x86)\Bitcoin\bitcoin-qt.exe -zapwallettxes

you might have to change this slightly depending where you installed core. Once you did this, just click ok and core will start rescanning all known blocks for your transactions. This can take a few minutes depending on your CPU and disk speed. Afterwards the conflicting TX should be gone and your wallet back to normal.

Thank you very much, this helped and the transactions has been removed.

[neonshium]

Op's both the stated transaction were not found in block-chain. So what is really going on. At least either one transaction should be picked by any blocks. I guess there would be a new kind of malleability attacks instead of a duplicate transaction-ID.

[shorena]

Op's both the stated transaction were not found in block-chain. So what is really going on. At least either one transaction should be picked by any blocks. I guess there would be a new kind of malleability attacks instead of a duplicate transaction-ID.

https://www.blocktrail.com/BTC/tx/4480c906a09ea358a2b5c0345af646f8b9a544043b870d787d37a8fcafcd470b

628 confirmations. The format OP posted above has an extra "-000" at the end of the TX ID. Bitcoin core shows them like that.