WARNING: Double check your transactions even when you only bump the fee (RBF)

[CryptSafe]

No one should be doing this in 2026, let Electrum official website direct you to the right Electrum wallet on Playstore, what if there is a fake or replicate Electrum wallet on playstore already? I was a victim of fake crypto wallet in 2020 or so, it cost me thousands of dollars, I went into Playstore and use their search engine to find a crypto wallet and it was fake with positive reviews, it was since that time that I stopped trusting reviews online and also stop using Playstore to find apps direct, it's not safe.

Sorry about your experience, sometimes things happens for us to learn our lesson from. Although I have had my own share of such in the past but not directly to this nature. This is why I am being very careful whenever I want to download apps that holds finds or any important information belonging to me. These days, google play store is no longer safe to download sensitive Apps like electrum etc. it is best to visit the genuine and original website to download apps of such nature because such can guarantee the safety of your assets. The if they already have such App on Google Play store, you could be redirected there from the original website to google play store to download the app or you download it from the website direct.

[BlackHatCoiner]

With the false positives that need to exist for privacy reasons, the bandwidth consumption and processing power consumed grows.

The bandwidth consumption and processing power are largely exaggerated. It takes as low as just a few hundred megabytes to support compact block filters. For today's standards, this is nothing. Waiting a few more minutes the first time you enter your wallet is worth the random entities you let scrutinize your wallet otherwise.

It's worth mentioning that it improves privacy it doesn't guarantee it. There are still shortcomings in that approach as well.

There is marginal privacy degradation between compact block filters and classic full node. There is massive difference between compact block filters and classic SPV.

[NefiSwap]

One thing nobody mentioned yet, from the side of the service that receives the coins.

When you bump the fee with RBF, the txid changes and the old one will never confirm. So if you sent to an exchange or a merchant and support asks for your txid, take it from your wallet history or a block explorer after the bump, not the one you copied before. Otherwise they look up a tx that has been replaced, and it looks like your coins disappeared.

Nobody mentioned it here because the OP actually understands that many members here understand what an RBF or any bump fee option means. The RBF itself means Replace-By-Fee and that tells everything. In the past when the nodes haven’t implemented the full RBF, both transactions do exist with the one which doesn’t get confirmed invalidate and it is mostly the first transaction because nodes give priority to transaction fees.

As for the TXID to give out after RBF, yes you should give out the new TXID after the RBF is done, but even if you give someone the earlier TXID and they decides to check it up on explorer, the explorers will still tell you that the transaction has been replaced and will even direct you to the new transaction. So even the old TXID isn’t actually wrong.

The difference with the vulnerability that OP brought is that the old TXID doe’s not exist because it was never broadcasted by the node and even if you check it up on any explorer it doesn’t finds any transaction with that ID

Fair, mempool.space does show that a tx was replaced and links to the new one. My point was more about support teams. Many of them check the txid in their own node or deposit system, not on a public explorer, and there the old one simply doesn't exist. Sending the new txid from the start saves a round of "we can't find your transaction".

[Yamifoud]

It is better to take caution than to be sorry. And I don't just double-triple-check the fees but also the address and where to send them. I haven't been wrong yet, and I don't make it happen either.

But as a vulnerability issue arises, upgrading to the latest version is not just necessary but urgent. Even on other platforms, this means a lot and much more in our storage wallet, especially if we put everything on it.

One thing I would say—don't rush sending because this mostly bypasses the important detail we need to check.

[Swift_tr]

Thanks a lot for the reminder Pooya87... there's been times the habit of double checking my transactions before they are being initiated have saved me loosing some funds. No matter the situation, even if it's an address in your beneficiary list you have to recheck before initiating a transaction. Laziness shouldn't make you lose your money to attackers who could've changed the address if your device was hacked .

A lot of people have been victims to this lackadaisical behaviour of not double checking or even triple checking their crypto transactions and in the process lost some funds. It's even worse when you missed an alphabet or number or getting them mixed up probably due to typo errors. Let's be careful out there a d remember that it doesn't cost you anything to be security conscious.

[Agbamoni]

This could be the reason I sent a coin to an unknown address. To date, I'm still wondering how and who owns that address.
I suspect it happened when I bumped the fee using RBF for the transaction. From @pooya87 explanation, maybe that was when the address swap happened.

Thank you, @pooya87, for providing more clarity on my suspicion. I wasn't insane after all. Cross checking all processes before broadcasting a transaction is very important.

[nullius]

I'll never understand why Electrum and other major wallets never bought into the concept of compact block filters that protect user's privacy by connecting directly to the Bitcoin network and download blocks. It's 2026, and people are still connecting their wallets to an SPV server, who can scan and group all their addresses.

Not to go off-topic, but would you please recommend one?  As I said on page 1 of the present thread:

https://bitcointalk.org/index.php?topic=5597827.msg67279449#nullius_needs_a_new_wallet

Personal note:  This is of peculiar interest to me, as I’ve been slowly drafting a topic OP about my urgent need for a new light wallet.  Electrum wasn’t under consideration anyway, as I’m hoping for a BIP 157/158 wallet with TUI written in C or Rust.  I will add to my list of requirements, “The wallet must never in any circumstance accept facially invalid transactions from the network.”

I sometimes used to use a BIP 157/158 wallet many years ago—but they turned evil, or perhaps were evil all along... you know which one.  If you don’t, check my two most recent sent red tags.

Anyone who thinks these servers are run voluntarily by "community members" are living in 2012. This is 2026, and chain analysis has significantly developed since.

There is marginal privacy degradation between compact block filters and classic full node. There is massive difference between compact block filters and classic SPV.

This is why.  Especially if the wallet has proper handling of Tor circuit isolation via SOCKS5 username/password, and sends tx via a one-off connection to a P2P network peer on an isolated Tor circuit.  The latter is better than an originating full node’s broadcast privacy, even with the Poisson timer trick that Core uses to make it moderately more difficult to trace the transaction’s origin!

The bandwidth consumption and processing power are largely exaggerated. It takes as low as just a few hundred megabytes to support compact block filters. For today's standards, this is nothing. Waiting a few more minutes the first time you enter your wallet is worth the random entities you let scrutinize your wallet otherwise.

People who watch Youtube videos in HD and 4K will complain about this.  (Compare djb’s remarks about Classic McEliece’s BIG PUBLIC KEYS.)  People who browse the Web of bloated 12 MB webpages loaded with CPU-sucking JS tracker-ads and (other) malware will complain about this.

The bandwidth and CPU loads of compact block filters are not insignificant, but they’re much lower than a full node’s—and the disk requirement is so small.

From Electrum's official website:

You are overthinking the terminology. Light[weight] client, Thin client and SPV client are terms used to describe the same concept. That is a wallet software that relies on block headers, merkle trees and PoW security.
By definition Electrum is one even if the wiki article doesn't use that exact term (their website and docs both do).

Thank you for the information about what Electrum calls itself.  I stand corrected.

That said, I think that terminology needs to be precise.  What is the unambiguous term for what I’m calling “SPV”?  The unambiguous term for the Electrum Protocol is “Electrum Protocol”.

P.S. You have very good points in your comments and I'm not arguing against what should happen but it is different from what can happen.

Thanks.  You also make some good points in your comments, and it’s nice to discuss and debate these technical issues with mutual respect.

However, you could always open a PR and contribute to Electrum project to help fix the issues you think can be fixed.

Or I could always write my own wallet, LOL.

[SquirrelJulietGarden]

This could be the reason I sent a coin to an unknown address. To date, I'm still wondering how and who owns that address.
I suspect it happened when I bumped the fee using RBF for the transaction. From @pooya87 explanation, maybe that was when the address swap happened.

Thank you, @pooya87, for providing more clarity on my suspicion. I wasn't insane after all. Cross checking all processes before broadcasting a transaction is very important.

With Electrum wallet, you have many chances and times of checking details of your transaction. When you paste an address to the "Pay to" box, it's the first time you check details.

Then click on Pay, you will have a "New transaction" box to check details again.
Then you have Preview to click on and check details again.

Many steps to check details, and be sure that you are doing accurately for a transaction. Almost same with practice for Bumping the fee later.

[SamReomo]

It's good to run your own node, but many people use SPV wallets like Electrum, because they don't want to run a node.

The best thing you can do to protect yourself is to double-check (or even triple-check) your transactions before broadcasting them.

Having your own node is a plus point but I agree majority don't want to run a node due to many reasons, out of those one reason is the space that's needed to download the whole blockchain. Many people are still happy with 256 GB SSD or 512 GB SSD and such people can't run their own nodes that's why they have to use others nodes for the transactions.

I agree, the better approach is to check transactions and destination addresses multiple times before broadcasting them, as that's something everyone can do. Also to be on safe end one should always update Electrum or any other open source wallet to its latest version.

[Peanutswar]

I thought I am just overthinking things because before I commit a transaction I made a double/triple check the address such as verifying upon copy and pasting if the address are the same and even check the price in mempool if there is an sudden changes of the fees because I dont get want to get stuck the transaction in the chain but seems previous days the fees does not surge unlike before its seems like steady right now in 1-3 sat/byte.  Thanks for the heads up seems I need to make it up my electrum now its been a while since I used to transact.

[#CapsLOck]

As with checking the address of the recipient. It's vital to check the change output. Several outputs can be included in a transaction. And users should check the destination of each of their funds prior to signing the transaction. This incident also illustrates the need to have wallet software. Rather than purely relying on users to identify suspicious transactions.

[pooya87]

That said, I think that terminology needs to be precise.

I completely agree. But unfortunately many concepts in Bitcoin are not clearly defined.

For example, what do you call old bitcoin core versions? Full node? Non-upgraded full node? Legacy node?
Any old version that is before the latest soft fork is no longer fully verifying everything since they don't have the new consensus rules. In cases like pre-SegWit versions (pre 0.18 IIRC) these nodes don't even receive parts of the transactions (the witness that is stripped) so they don't even store the full blockchain.

So they can no longer be referred to as "full" nodes.
Legacy node is closer but the term "legacy" could mean many things. It is not clear that they do not verify everything and are not full nodes.

[BlackHatCoiner]

Not to go off-topic, but would you please recommend one?

Wasabi Wallet. I have not come across any other as good, and this one comes with the best and most liquid coinjoin implementation, so you can gain on-chain privacy as well.

People who watch Youtube videos in HD and 4K will complain about this.  (Compare djb’s remarks about Classic McEliece’s BIG PUBLIC KEYS.)  People who browse the Web of bloated 12 MB webpages loaded with CPU-sucking JS tracker-ads and (other) malware will complain about this.

This is just a reminder that this is real money, and your life is tied to it. This is more important than a mere inconvenience in the browser. Money privacy is not a "nice to have" but a necessity.

[Somegory]

This is scary and thank you OP for sharing, I've never come across this type of attack before I would have become a victim of I found myself in such situation because how the hell will I know that transaction can be intercepted while adjusting RBF?

There is also something called whitelisting, this have saved me from clipboard malware attack where the address you copied was changed to something else when you pasted it.

If you already whitelisted the address or addresses on a crypto exchange they will process the transactions without the need to verify for you over and over, once it's whitelisted you are good to go.

[nullius]

That said, I think that terminology needs to be precise.

I completely agree. But unfortunately many concepts in Bitcoin are not clearly defined.

So, let’s define concepts more clearly.  Be pedantic! 

For example, what do you call old bitcoin core versions? Full node? Non-upgraded full node? Legacy node?
Any old version that is before the latest soft fork is no longer fully verifying everything since they don't have the new consensus rules.

Good question.  Off the top of my head, “legacy node”.  It’s soft-deprecated, gently frowned upon—but Core developers bend over backwards to avoid forking it off the network unless absolutely necessary.

I appreciate that—speaking as an altcoin user who’s had the problem of, “Oh, no!  The network hardforked while I wasn’t following the news, I can’t access my money, I need to buy food right now, the new version of my wallet crashes with an inscrutable error, and now, I’m using nm to try to debug a library versioning problem while I’m hungry and I can’t use my money.”  Literally happened.  Not exaggerating.  I strongly urge Bitcoin legacy nodes to upgrade, but it’s good for people always to have access their own money.

Wasabi Wallet.

Not anytime after 2022 (follow-up).  Now, absolutely not.  I don’t want to derail this thread, so please just see my trust page’s sent feedback for 2026-10-27.

I sometimes used to use a BIP 157/158 wallet many years ago—but they turned evil, or perhaps were evil all along... you know which one.  If you don’t, check my two most recent sent red tags.

This is just a reminder that this is real money, and your life is tied to it. This is more important than a mere inconvenience in the browser.

My implication (and djb’s) was that people waste enormous amounts of bandwidth and CPU on sheer nonsense that no one needs, like Youtube and bloated web apps—then complain about Classic McEliece’s megabyte public keys... or light wallet protocols that take moderately more bandwidth and CPU than the Electrum Protocol.

It is a special case of the classic Dancing Pigs problem.

I almost never watch HD/4K dancing pigs on Youtube, I absolutely never watch Tiktok, I surf the web >99% with JavaScript disabled, and I use an ad blocker in iron-fisted fascist mode when I need to enable JS in a non-Tor browser.  For fuck’s sake, I like the Bitcoin Forum because its pages are still so lightweight (thanks, theymos).  And I want a wallet with no GUI, and definitely not written in bloated C#.

Rant mode on:  I think I have a right to nitpick over relatively moderate amounts of bandwidth and CPU use!  Nonetheless, I’d be willing to accept a Bitcoin adaptation for transparent UTXOs of what Zcash’s light wallet protocol does only for shielded notes.  That would be a sort of compact blocks.  It’s used by all Zcash light wallets, because a privacy coin needs to be serious about privacy; each Zcash phone wallet downloads a compact version of every shielded note, and spends CPU trial-decrypting it—maybe repeatedly, if that wallet has more than one shielded viewkey.  Light wallet users don’t die from this.  Compact block filters are much lighter—negligible by comparison, except that you then need to download a whole (non-compact) block anytime you may have received a transaction.  Well, if you receive many transactions, it means you get lots of money; poor people who never receive money will not have this problem.  Don’t complain!

[BlackHatCoiner]

Not anytime after 2022 (follow-up).  Now, absolutely not.  I don’t want to derail this thread, so please just see my trust page’s sent feedback for 2026-10-27.

I neither want to derail this thread, and I probably know better than anyone in this thread what happened with Wasabi four years ago, but all I can say is that the company which it inherited this bad reputation from is now gone for good and there are only Bitcoin developers who are working on this, voluntarily with donations. It's now just open-source, more robust, with coordinators run by the contributors, and there is virtually no sign that some State-level actor is sleeping in bed with them.

[nullius]

I neither want to derail this thread, and I probably know better than anyone in this thread what happened with Wasabi four years ago, but all I can say is that the company which it inherited this bad reputation from is now gone for good and there are only Bitcoin developers who are working on this, voluntarily with donations.

Thanks for the clarification.  You’ve got rep.  I will look into it.

I still want a lightweight BIP 157/158 (compact block filter) wallet with TUI, written in C or alternatively, Rust.  (Language makes a real difference, because I like to customize things in private branches; both my Tor daemon (C) and my Zcash wallet (Rust) actually run with some little local patches.)  The only thing I liked about Wasabi was its implementations of receiving (compact block filters) and sending (one-off connection to peer on isolated Tor circuit).  I only used its CoinJoin a few times, to test it; I don’t need any CJ.  I strongly disliked its GUI (which didn’t even use OS widgets as of v1), and it was heavy and slow.  But the privacy of simply receiving and sending bitcoins was excellent for a light wallet!

* nullius ♥️ compact block filters.

(Apologies to pooya87.  I do intend to make my own thread about my wallet needs.  The very long rant about wallets will go there!)