broken /eth/v1/beacon/blob_sidecars/ endpoint in 6.1.2: multiplication overflows

[mask-pp]

Describe the bug

t=2025-10-14T10:21:21+0000 lvl=error msg="Engine failed temporarily, backing off sequencer" err="derivation failed: temp: failed to fetch blobs: failed to get blob sidecars for L1BlockRef 0xf4dae2eba48afb9b43a47974bd86caf471cc2810ea44a619e94e537a80f04bb0:9408243: failed to fetch blob sidecars for slot 12799942: failed request with status 500: {"message":"Internal server error: could not calculate Fulu start slot: start slot calculation overflows: multiplication overflows","code":500}"

Has this worked before in a previous version?

🔬 Minimal Reproduction

No response

Error

Platform(s)

Linux (x86)

What version of Prysm are you running? (Which release)

v6.1.2

Anything else relevant (validator index / public key)?

No response

[inoue-uh]

voting up this one, i have absolutely similar issue with my arbitrum nitro and optimism op-geth mainnet full nodes that use prysm as l1

[nalepae]

Thanks for the report. Looking at it.

[nalepae]

OK I reproduce the issue. Working on a fix. Sorry for the inconvenience.

[nalepae]

Fixed in develop with:

• Fix /eth/v1/beacon/blob_sidecars/ beacon API if the fulu fork epoch is set to the far future epoch. #15867

We are currently soaking a new release for this fix.

[seeforschauer]

thank you, experiencing the same issue with my arbitrum nitro.