CVE-2026-55434: Coder Coder DoS Vulnerability

CVE-2026-55434 Overview

CVE-2026-55434 is a denial of service vulnerability in Coder, a platform that provisions remote development environments through Terraform. The flaw resides in the AI Bridge provider handlers, which read HTTP request bodies using io.ReadAll without enforcing a maximum size limit. An authenticated user with AI Bridge access can submit an arbitrarily large request body to exhaust server memory. The vulnerability affects Coder versions 2.33.0 through 2.33.7 and 2.34.0 through 2.34.1. Coder released fixes in versions 2.33.8 and 2.34.2. The weakness is classified as [CWE-770] (Allocation of Resources Without Limits or Throttling).

Critical Impact
An authenticated attacker with AI Bridge access can exhaust server memory and cause a denial of service against the Coder deployment.

Affected Products

Coder versions 2.33.0 through 2.33.7
Coder versions 2.34.0 through 2.34.1
Deployments exposing AI Bridge provider endpoints

Discovery Timeline

2026-07-07 - CVE-2026-55434 published to NVD
2026-07-08 - Last updated in NVD database

Technical Details for CVE-2026-55434

Vulnerability Analysis

Coder's AI Bridge feature proxies requests between developer environments and AI service providers. The provider handlers ingest client-supplied HTTP request bodies before forwarding or processing them. In the affected versions, these handlers invoke io.ReadAll on the request body without wrapping the reader with http.MaxBytesReader or an equivalent size guard.

Because io.ReadAll grows its internal buffer until end-of-stream, an attacker can stream a request body of arbitrary size into the process. The Go runtime allocates progressively larger byte slices to hold the payload, which drives the Coder server toward memory exhaustion. Under sufficient load or with a single sufficiently large request, the process can be killed by the operating system's out-of-memory handler.

Exploitation is limited to availability. The vulnerability does not disclose data or allow code execution, and it requires an authenticated session with AI Bridge access.

Root Cause

The root cause is missing input size validation on request bodies within the AI Bridge provider handler code path. Reading untrusted input with io.ReadAll and no upper bound is a well-known pattern for resource exhaustion in Go HTTP services.

Attack Vector

The attack is network-based and requires low-privilege authenticated access. An attacker sends a POST request to an AI Bridge provider endpoint with an oversized body, such as a large JSON document or streamed payload. The server accepts the entire body before rejecting or processing it, allocating memory proportional to the payload size. Repeated or concurrent requests amplify the impact and can bring down the Coder control plane.

No verified public proof-of-concept code is available. See the GitHub Security Advisory GHSA-f5vp-w269-392g and the remediation pull request for technical details.

Detection Methods for CVE-2026-55434

Indicators of Compromise

HTTP requests to AI Bridge provider endpoints with Content-Length values or transferred payload sizes far exceeding typical API traffic.
Repeated large POST requests originating from a single authenticated user or session token.
Coder server processes terminated by the operating system out-of-memory (OOM) killer, or sudden spikes in resident memory usage.

Detection Strategies

Alert on AI Bridge endpoint requests exceeding a defined byte threshold, correlated with the authenticated user identity.
Monitor Coder pod or host memory pressure and correlate spikes with inbound request volume to AI Bridge routes.
Review authentication logs for AI Bridge access from accounts that do not normally interact with AI features.

Monitoring Recommendations

Enable request-size logging on the reverse proxy or ingress controller fronting Coder to capture body sizes per endpoint.
Track container restart counts and OOM events in orchestration platforms such as Kubernetes.
Baseline normal AI Bridge request payload sizes and alert on statistical outliers.

How to Mitigate CVE-2026-55434

Immediate Actions Required

Upgrade Coder deployments to version 2.33.8 or 2.34.2 as soon as possible.
Audit the list of users with AI Bridge access and remove entitlements that are not required.
Enforce rate limiting and request-size caps at the ingress layer in front of Coder until patching is complete.

Patch Information

Coder addressed the issue in release v2.33.8 and release v2.34.2. The remediation, tracked in pull request #26164, applies a bounded reader to AI Bridge provider handlers so that oversized bodies are rejected before memory is exhausted. Refer to the GitHub Security Advisory GHSA-f5vp-w269-392g for full advisory content.

Workarounds

No vendor-supplied workarounds exist; upgrading is the only complete fix.
As a compensating control, configure the upstream reverse proxy or ingress to cap request body sizes on AI Bridge routes.
Restrict AI Bridge endpoint access to trusted network segments or specific user groups until patches are applied.

bash

# Example NGINX ingress compensating control to cap AI Bridge request bodies
location /api/v2/aibridge/ {
    client_max_body_size 1m;
    proxy_pass http://coder-upstream;
}