CVE-2026-33582: Apache Answer DOS Vulnerability

CVE-2026-33582 Overview

CVE-2026-33582 is an Unrestricted Upload of File with Dangerous Type vulnerability [CWE-434] in Apache Answer through version 2.0.0. The flaw allows an authenticated user to upload a crafted TIFF image that triggers excessive memory allocation during image decoding. The resulting resource exhaustion crashes the server process, producing a denial-of-service condition. Apache addressed the issue in Apache Answer 2.0.1.

Critical Impact
An authenticated attacker can crash the Apache Answer server process by uploading a single crafted TIFF file, disrupting availability of the Q&A platform for all users.

Affected Products

Apache Answer versions through 2.0.0
Apache Answer deployments accepting user image uploads
Self-hosted Apache Answer instances with authenticated user registration

Discovery Timeline

2026-06-09 - CVE-2026-33582 published to NVD
2026-06-09 - Apache mailing list and OSS-Security disclosure published
2026-06-10 - Last updated in NVD database

Technical Details for CVE-2026-33582

Vulnerability Analysis

Apache Answer is an open-source community Q&A platform that supports image uploads for user content. The vulnerability resides in the image decoding path invoked when authenticated users submit images. A specially crafted TIFF file causes the decoder to allocate an excessive amount of memory while parsing image metadata or pixel data.

Because the decoder does not validate or constrain allocation sizes derived from attacker-controlled image headers, the process consumes available memory until the operating system terminates it or the runtime aborts. This produces an availability impact on the host service while leaving confidentiality and integrity intact.

Root Cause

The root cause is missing validation of file type and resource bounds during the image upload and decode workflow. Apache Answer accepts the TIFF format and passes the file to a decoder that trusts header-supplied dimensions and strip values. Without size sanity checks or allocation limits, malformed TIFF structures coerce the decoder into requesting memory far beyond legitimate image needs.

Attack Vector

An attacker requires a valid authenticated session on the target Apache Answer instance. The attacker uploads a crafted TIFF image through any feature that accepts image attachments, such as question or answer creation, profile avatars, or comments. The server-side image processor decodes the file, allocates the requested memory, and crashes. Repeating the upload keeps the service unavailable.

// No verified public proof-of-concept is available.
// Refer to the Apache advisory for technical details:
// https://lists.apache.org/thread/3sgpx4cwsgpnt66xv3cqvtc8z4st1kbq

Detection Methods for CVE-2026-33582

Indicators of Compromise

Unexpected termination or restart of the Apache Answer application process shortly after a file upload request
Spikes in resident memory usage by the Answer process correlated with POST requests to upload endpoints
Authenticated upload requests submitting TIFF files (Content-Type: image/tiff or .tif/.tiff extensions) from low-reputation accounts
Out-of-memory (OOM) killer entries in dmesg or system logs referencing the Answer process

Detection Strategies

Monitor application logs for repeated upload failures, crashes, or worker restarts following image submissions
Inspect reverse proxy and web server access logs for upload requests carrying TIFF MIME types or extensions
Alert on rapid sequential uploads from a single authenticated user identifier
Correlate process exit events with preceding HTTP upload requests using centralized log analysis

Monitoring Recommendations

Track memory consumption per Answer worker process and alert on sudden allocations exceeding configured thresholds
Aggregate web application logs into a SIEM and build queries for TIFF uploads tied to subsequent service restarts
Enable container or systemd restart counters as a leading indicator of repeated DoS attempts
Review newly registered accounts performing immediate image uploads as a potential abuse pattern

How to Mitigate CVE-2026-33582

Immediate Actions Required

Upgrade Apache Answer to version 2.0.1 or later, which contains the official fix
If upgrade cannot be performed immediately, restrict registration and require manual approval for new accounts
Place a reverse proxy or web application firewall in front of Answer to block or filter TIFF uploads
Configure process supervisors to automatically restart the Answer service after a crash to limit downtime

Patch Information

Apache released Apache Answer 2.0.1 to address CVE-2026-33582. The fix is announced in the Apache Mailing List Thread and the OpenWall OSS Security Posting. Administrators should upgrade promptly and verify the running version after deployment.

Workarounds

Reject TIFF uploads at the reverse proxy by filtering on file extension and Content-Type headers
Apply per-process memory limits using cgroups, systemdMemoryMax, or container resource limits to contain allocation spikes
Rate-limit upload endpoints per authenticated user to reduce the impact of repeated abuse
Disable image uploads for untrusted user roles where business requirements allow

bash

# Example: enforce a memory limit on the Apache Answer systemd service
# Edit the unit file or use a drop-in override
sudo systemctl edit answer.service

# Add the following under [Service]
# MemoryMax=1G
# MemoryHigh=768M
# Restart=on-failure
# RestartSec=5s

sudo systemctl daemon-reload
sudo systemctl restart answer.service