Ledger Ethereum App Signing Flaw Explained

Video transcript

A hardware wallet promises the screen shows what the key signs. In August 2026, Ledger disclosed a flaw that could break that promise.

The bug sat in Ledger's Secure SDK, not the firmware. The fix shipped before disclosure, and Ledger reports no evidence of exploitation.

During review, the SDK let the computer send another command. If an app missed a state check, it could overwrite the shown values, and approval signed them.

The attacker had to control the command channel. Ledger lists three routes: a malicious or compromised wallet app, a hostile web page, or malware on the computer.

Ethereum app version one point two two point two closed it on August 13. Version one point two two point three fixed two other signing flaws.

Ledger says a firmware update alone does not establish that affected apps were replaced. Update the app in Ledger Live, then confirm its version on the device.

Multisig is no cure. A shared device flaw can repeat across signers. Record each signer's app version, follow Ledger's bulletins, sign from a dedicated machine, and check hashes independently.

Guardian's Managed Security lists this flaw among its advisories. Where a disclosure reaches your system, an engineer confirms exposure and helps you patch it.

Read the full article for the timeline and all three bulletins, or talk to Guardian at guardian.security.

A hardware wallet makes one promise: what the screen shows is what the key signs.

In August 2026, Ledger disclosed a flaw that could break that promise, first fixed in its Ethereum app. The fix shipped before the flaw was public, and Ledger says it has no evidence of exploitation.

For teams whose multisig signers use Ledger devices, the question is practical: which app version is each signer running?

What Happened

On August 27, 2026, Ledger published Security Bulletin 023. Its title: "Command interleaving during an on-screen review could desynchronise the display from the signature."

The flaw sat in the Ledger Secure SDK that device apps compile against, through a regression introduced in August 2025. The device OS and firmware were not affected.

Ethereum app 1.22.2, published August 13, added state guards that closed it. SDK v26.6.1 fixed the root cause on August 21.

Who found it

Ledger credits its own continuous security review. The flaw still went public before the bulletin.

On August 22, security company TestMachine posted that its Azimuth AI tool had found the bug and validated it on a Ledger Flex, crypto.news reported.

Ledger CTO Charles Guillemet replied on August 23: "It was fixed and deployed two weeks ago." He said Ledger's Donjon team had found it with AI-powered tools.

The accounts differ. TestMachine said it shared and verified the finding with Ledger. Guillemet said it reached Ledger's bounty program only after the fix shipped.

How the Flaw Worked

Signing on a Ledger runs in steps. The computer sends the transaction, the device shows it, and the user approves or rejects.

While the user reviews, the app holds the signing parameters in memory and waits, Ledger's bulletin explains.

The SDK did not stop the computer from sending another command during that wait.

If an app missed a state check on any one entry point, the new command could overwrite values the user had already seen.

The approval then signed the modified values. Ledger classifies it as a time-of-check to time-of-use flaw (CWE-362).

Ledger describes a chunked technique that made it practical:

1. The attacker sends a first chunk that overwrites leading fields, such as the derivation path.
2. It withholds the rest of the payload.
3. The screen keeps its earlier values, and the interrupted command shows no error.

Nothing on the device signals the substitution, Ledger says.

Who could use it

The attacker had to control the APDU exchange, the command channel between computer and device. Ledger lists three routes:

• A malicious or compromised wallet application.
• A hostile web page holding a WebHID or WebUSB connection.
• Malware on the connected computer.

Crypto Briefing gave an example: approving what looks like a small token transfer while authorizing unlimited token approvals to an attacker.

Ledger says the reach of any instance is bounded by what the affected command can express.

Timeline and Impact

Affected versions. Ledger lists them by SDK, not by app: applications built against SDK releases from August 2025 through v26.6.0. Apps that validate state on every asynchronous entry point were not exposed.

Losses. Ledger says it has no evidence of exploitation against users. As of August 24, no confirmed thefts had been reported, per crypto.news and Crypto Briefing.

Two more bulletins the same day

• LSB 024 (app 1.19.0 to 1.22.2): arrays over 255 elements were miscounted, so the screen could show one operation while the signature covered all.
• LSB 025 (app 1.20.0 to 1.22.2): in a swap, a token approval could pass as a payment and be signed without being shown.

Both were fixed in Ethereum app 1.22.3, published August 25.

Later releases, 1.22.4 (September 8) and 1.22.5 (September 17), fixed other, separate issues. Neither is the LSB 023 fix.

What It Shows

The screen is a security boundary, and software sits behind it. Device apps get bugs, and fixes arrive as app updates.

• Firmware is not enough. Ledger says updating firmware alone does not establish that affected apps were replaced.
• Release notes can be terse. The changelog lists 1.22.2 (dated August 12) only as "Security issues." Details came two weeks later.
• The host matters. Every route Ledger lists runs through the computer or page the signer uses.
• Multisig is not a cure. Ledger's LSB 024 notes a shared device flaw makes "several apparently independent device confirmations" repeat one failure.

A checklist for signer teams

1. Record each signer's device model and Ethereum app version.
2. Update through Ledger Live, then confirm the app version on the device itself.
3. Follow Ledger's security bulletins and the Ethereum app changelog.
4. Sign from a dedicated machine, not a daily laptop.
5. Check transaction hashes on a second, independent tool before signing.

For more, read what blind signing is and our guide to hardware wallets for multisig signers. Related advisory: the Cosmos EVM exploit explained.

How Managed Security Covers This

Guardian's Managed Security walkthrough lists this flaw among its recent advisories, summed up as "Transactions could be swapped."

Under Managed Security, Guardian "ingests vulnerability disclosures in real time and matches them against your system." Where one reaches a team, an engineer confirms the exposure and works with them to patch it.

The same page lists multisigs and signing services in its 24/7 coverage. Guardian's security operations team reviews every multisig transaction before it is signed.

Onboarding, per the page, puts controls and verification gates in place from day one.

Frequently Asked Questions

Which Ledger Ethereum app version fixes the signing flaw?

Version 1.22.2, published August 13, 2026, fixed it. Two other signing flaws were fixed in 1.22.3 on August 25, and later releases fix separate issues. Install the latest version and confirm it on the device.

Were any funds stolen through the flaw?

Ledger says it has no evidence of exploitation against users. As of August 24, 2026, no confirmed thefts tied to the flaw had been reported, per crypto.news and Crypto Briefing.

Does a Ledger firmware update fix it?

No. Ledger says the firmware was not affected, and the fix comes as an app update. Update the Ethereum app through Ledger Live, then check the app version on the signer.

Who found the Ledger Ethereum app flaw?

Ledger says its internal continuous security review found it. On August 22, 2026, TestMachine said its Azimuth AI tool had found the bug. Ledger's CTO said the fix had already shipped.

Sources

• Ledger Donjon: Security Bulletin 023, Command interleaving during an on-screen review could desynchronise the display from the signature (August 27, 2026)
• Ledger Donjon: Security Bulletin 024, Clear-signing bypass via array-count truncation in the Ethereum app (August 27, 2026)
• Ledger Donjon: Security Bulletin 025, Swap flow accepted a token approval in place of a payment (August 27, 2026)
• LedgerHQ on GitHub: Ethereum app changelog, 1.22.2 to 1.22.5 (read November 2026)
• crypto.news: Ledger says Ethereum signing flaw was already fixed (August 24, 2026)
• Crypto Briefing: Ledger fixes vulnerability in Ethereum app's signing flows (August 24, 2026)
• Guardian: Managed Security