CVE-2026-42154

Impact

The remote read endpoint (/api/v1/read) does not validate the declared decoded length in a snappy-compressed request body before allocating memory. An unauthenticated attacker can send a small payload that causes a huge heap allocation per request. Under concurrent load this can exhaust available memory and crash the Prometheus process.

Patches

Has the problem been patched? What versions should users upgrade to?

Fixed in 3.11.3 and 3.5.3 LTS. Users should upgrade to these versions or later.

Workarounds

User who can not upgrade can place Prometheus behind a reverse proxy or firewall that requires authentication before requests reach /api/v1/read.