OpenBao has Decompression Bomb via Unbounded Copy in OCI Plugin Extraction (DoS) (CVE-2026-39396)

OpenBao's OCI plugin downloader function ExtractPluginFromImage() in versions before 2.5.3 performs decompression of plugin binaries from container images by streaming decompressed tar data via io.Copy without limiting the number of bytes written to disk. An attacker who controls or compromises the OCI registry referenced in the victim's configuration can supply a crafted container image containing a decompression bomb. This bomb decompresses to an arbitrarily large file, exhausting disk space on the victim system. The SHA256 integrity check occurs only after the full file is written, so the denial of service occurs before detection. The vulnerability allows an attacker to replace a legitimate plugin image without needing to alter its signature. The issue is resolved in OpenBao version 2.5.3.

An attacker with control or compromise of the OCI registry can cause a denial of service on the victim system by serving a crafted container image that decompresses to a very large file, exhausting disk space. This can disrupt normal operation of OpenBao by preventing plugin extraction and potentially impacting system stability. The integrity check does not prevent the attack because it occurs after the decompression and disk write, allowing the decompression bomb to cause damage before detection.

Upgrade OpenBao to version 2.5.3 or later, which contains a patch that addresses this decompression bomb vulnerability by imposing limits on the decompression process. Until upgraded, avoid using OCI registries that are not fully trusted or could be compromised. No other mitigations are specified.