GHSA-4rmq-mc2c-r495 Babylon Incorrect FP inactive accounting in costaking creates “phantom stake” that earns rewards after BTC unbond
A state consistency bug allows attackers to earn costaking rewards without backing BTC by exploiting a race condition during unbonding.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is GHSA-4rmq-mc2c-r495?
GHSA-4rmq-mc2c-r495 is a vulnerability in github.com/babylonlabs-io/babylon, published on 9 Dec 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Summary
A state consistency bug in x/costaking can leave a BTC delegator with non-zero ActiveSatoshis (Phatom Stake) even after they have fully unbonded their BTC delegation, if their Finality Provider (FP) drops out of the active set in the exact same babylon block height. This creates a “phantom stake”: the delegator’s BTC capital is withdrawn, the FP is inactive, but costaking continues to treat the delegation as active BTC stake allowing ongoing rewards accrual without backing BTC.
Impact
An address can keep earning costaking rewards with zero BTC staked.
Reported by @BottyBott.
Which versions are affected by GHSA-4rmq-mc2c-r495?
12 open source packages ship an affected version, including github.com/babylonlabs-io/babylon, github.com/babylonlabs-io/babylon/v2 and github.com/babylonlabs-io/babylon/v3.
| Package | Affected | Fixed in |
|---|---|---|
github.com/babylonlabs-io/babylon Go | All versions | None |
github.com/babylonlabs-io/babylon Go | All versions to 1.1.0 | None |
github.com/babylonlabs-io/babylon Go | All versions to 1.1.0 | None |
github.com/babylonlabs-io/babylon/v2 Go | All versions | None |
github.com/babylonlabs-io/babylon/v2 Go | All versions to 2.3.2 | None |
github.com/babylonlabs-io/babylon/v2 Go | All versions to 2.3.2 | None |
6 more packages
github.com/babylonlabs-io/babylon/v3 Go | All versions | None |
github.com/babylonlabs-io/babylon/v3 Go | All versions to 3.0.0-snapshot.250805a | None |
github.com/babylonlabs-io/babylon/v3 Go | All versions to 3.0.0-snapshot.250805a | None |
github.com/babylonlabs-io/babylon/v4 Go | All versions | 4.2.0 |
github.com/babylonlabs-io/babylon/v4 Go | All versions | 4.2.0 |
github.com/babylonlabs-io/babylon/v4 Go | All versions | 4.2.0 |
How do I fix GHSA-4rmq-mc2c-r495?
Apply the vendor's patch.
Is GHSA-4rmq-mc2c-r495 being exploited?
There is no known exploitation of GHSA-4rmq-mc2c-r495 in the wild and no public exploit code.
Sources
Also known as GO-2025-4214.