3.1

CVSS Score

3.1

-

CVSS Score

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CVE-2026-39396

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

OpenBao is an open source identity-based secrets management system. Prior to version 2.5.3, ExtractPluginFromImage() in OpenBao's OCI plugin downloader extracts a plugin binary from a container image by streaming decompressed tar data via io.Copy with no upper bound on the number of bytes written. An attacker who controls or compromises the OCI registry referenced in the victim's configuration can serve a crafted image containing a decompression bomb that decompresses to an arbitrarily large file. The SHA256 integrity check occurs after the full file is written to disk, meaning the hash mismatch is detected only after the damage (disk exhaustion) has already occurred. This allow the attacker to replace legit plugin image with no need to change its signature. Version 2.5.3 contains a patch.

(GitHub Advisory)

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CVE-2026-39396

CVE-2026-39396:

3.1

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
github.com/openbao/openbao	go	< 0.0.0-20260420180337-2b2a901aa9f7	0.0.0-20260420180337-2b2a901aa9f7

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability is a classic 'decompression bomb' scenario leading to denial-of-service. It exists in the OCI plugin downloader of OpenBao, specifically within the ExtractPluginFromImage function located in helper/pluginutil/oci/downloader.go. The function's purpose is to extract plugin binaries from OCI container images. The flaw was in its use of io.Copy to write the decompressed data from a tar stream to the filesystem without imposing any limits on the size of the output file. An attacker could craft a malicious OCI image with a highly compressed file that would expand to an enormous size upon extraction. When OpenBao is configured to download this malicious plugin, the ExtractPluginFromImage function is invoked. The unbounded io.Copy would then consume all available disk space, causing a DoS that affects not only the OpenBao instance but also any other applications running on the same host. The provided patch confirms this analysis by introducing several safeguards in the ExtractPluginFromImage function: it adds a check against a new configurable maximum file size (plugin_download_max_size), verifies available disk space before writing, and crucially, wraps the reader in io.LimitReader to strictly enforce the size declared in the tar header during the copy operation. Therefore, PluginDownloader.ExtractPluginFromImage is the precise function where the vulnerability is located and which would be active during exploitation.

Vulnerable functions

PluginDownloader.ExtractPluginFromImage

helper/pluginutil/oci/downloader.go

This function extracts a plugin binary from an OCI image. The original code used `io.Copy` to write the decompressed tar data to a file without any size limits. An attacker could provide a malicious OCI image containing a 'decompression bomb' (a small, highly compressed file that expands to a very large size). When this function processes the malicious image, the unbounded copy operation would write an extremely large file to disk, exhausting all available disk space and causing a denial-of-service (DoS) on the server.

Vulnerability Intelligence
Miggo AI

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WAF Rule

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Reasoning

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