Technical Analysis of CVE-2026-111497: Pinned WordPress Image RCE Proof of Concept

Overview of CVE-2026-111497

A proof-of-concept (PoC) repository has been published detailing a target-specific remote code execution (RCE) chain tracked as CVE-2026-111497. The research demonstrates unauthenticated command execution against a specific pinned Docker Official Image for WordPress. According to the published documentation, the mechanism relies on a combination of an XML-RPC pingback request and a manipulated Brotli decoding stream.

It is important to note that the findings apply exclusively to the tested image digest and make no claims regarding current WordPress images, other digests, or memory errors in WordPress Core.

How the Attack Vector Operates

The reported chain involves several distinct technical conditions:

• Inbound XML-RPC Request: A single unauthenticated `pingback.ping` request triggers WordPress to fetch an attacker-controlled URL twice during the same PHP request.
• Decoder Corruption: The first HTTP response corrupts a PHP handler through a malformed Brotli data stream. Specifically, it copies bytes from a live system handler pointer into the `strtolower` handler, leveraging the fact that both pointers share the same ASLR-loaded `libphp.so` base.
• Retry and Execution: After encountering a content encoding error, the HTTP transport retries without content decoding. The subsequent header reaches the modified handler, starting a fixed Bash command that reads a synthetic flag file, which is then returned in the XML-RPC response.

Prerequisites and Environment Requirements

The reported lab environment relies on strict constraints, including:

• Reachable `/xmlrpc.php` with `pingback.ping` enabled.
• A functioning post that accepts pingbacks and allows WordPress to fetch external URLs.
• Specific versions of Brotli, PHP, glibc, cURL, Requests, Apache, and the system memory allocator.
• Linux amd64 running rootless Podman with ASLR mode 2 enabled.

Verification and Mitigation Strategies

Security researchers and system administrators can review the repository scripts, such as `verify.sh` and `generate_payloads.py`, to inspect payload constants and serialization stages using the Python standard library.

To address potential exposure, administrators should apply the following steps:

• Update affected Brotli packages to vendor-fixed versions (such as upstream branches 1.0.10, 1.1.1, or 1.2.1, or appropriate distribution backports).
• Restart or redeploy all processes that loaded the vulnerable decoder libraries.
• Disable unused XML-RPC pingbacks and remove untrusted Brotli decoding paths until updates are fully applied.

Review official vendor advisories and changelogs to verify the exact status of installed packages.