CVE-2026-25122 Overview
A resource exhaustion vulnerability has been identified in apko, a tool that allows users to build and publish OCI container images built from apk packages. The vulnerability exists in the expandapk.Split function which drains the first gzip stream of an APK archive via io.Copy(io.Discard, gzi) without explicit bounds. When processing attacker-controlled input streams, this can force large gzip inflation work, leading to resource exhaustion and availability impact.
Critical Impact
An attacker can craft malicious APK archives that cause excessive CPU consumption during gzip inflation, potentially leading to denial of service conditions through process slowdown or timeouts.
Affected Products
- apko versions 0.14.8 to before 1.1.0
- OCI container image build pipelines using vulnerable apko versions
- Systems processing untrusted APK streams with apko
Discovery Timeline
- 2026-02-04 - CVE CVE-2026-25122 published to NVD
- 2026-02-05 - Last updated in NVD database
Technical Details for CVE-2026-25122
Vulnerability Analysis
The vulnerability resides in the Split function within apko's APK archive handling code. The function reads the first tar header from an APK archive, then drains the remainder of the gzip stream by reading directly from the gzip reader. The critical flaw is the absence of any maximum uncompressed byte limit or inflate-ratio cap, which means the function will process gzip data until the stream is exhausted, regardless of the output size.
This allows for a classic gzip bomb attack vector where a small compressed payload can expand to an enormous size during decompression. When a caller parses attacker-controlled APK streams, the system may be forced to spend excessive CPU time inflating maliciously crafted gzip data, resulting in denial of service conditions.
Root Cause
The root cause is classified as CWE-400 (Uncontrolled Resource Consumption). The expandapk.Split function lacks defensive programming measures such as:
- Maximum uncompressed byte limits
- Inflate ratio caps to detect gzip bombs
- Timeout mechanisms for decompression operations
- Resource consumption monitoring during stream processing
Without these safeguards, the function is vulnerable to algorithmic complexity attacks where the computational cost of processing input significantly exceeds the input size.
Attack Vector
The attack requires local access with user interaction (processing a malicious APK file). An attacker would craft a specially designed APK archive containing gzip-compressed data with an extremely high compression ratio. When a victim processes this archive using a vulnerable apko version, the Split function will attempt to decompress the malicious stream, consuming excessive CPU resources.
The security patch introduces limit readers for readers that consume data from external sources, as shown in the fix:
"chainguard.dev/apko/pkg/build"
"chainguard.dev/apko/pkg/build/types"
"chainguard.dev/apko/pkg/cpio"
+ "chainguard.dev/apko/pkg/options"
)
func buildCPIO() *cobra.Command {
Source: GitHub Commit Update
The patch adds the options package import which contains limit reader implementations to bound resource consumption when processing external data sources.
Detection Methods for CVE-2026-25122
Indicators of Compromise
- Unusual CPU spikes during APK archive processing
- Process timeouts or unresponsive container build operations
- Memory pressure or OOM events in apko build pipelines
- Abnormally large or suspiciously structured APK files in build directories
Detection Strategies
- Monitor apko process CPU utilization for anomalous sustained high usage
- Implement file size and compression ratio checks on incoming APK archives
- Set up alerts for build pipeline timeouts that may indicate resource exhaustion attacks
- Review logs for repeated failed or stalled APK processing operations
Monitoring Recommendations
- Enable resource monitoring on systems running apko build operations
- Implement rate limiting and resource quotas for APK processing workloads
- Configure alerting thresholds for CPU and memory consumption in CI/CD pipelines
- Track and analyze APK file characteristics before processing in production environments
How to Mitigate CVE-2026-25122
Immediate Actions Required
- Upgrade apko to version 1.1.0 or later immediately
- Audit systems for vulnerable apko versions between 0.14.8 and 1.1.0
- Review container build pipelines that process untrusted APK sources
- Implement resource limits on apko processes until patching is complete
Patch Information
The vulnerability has been patched in apko version 1.1.0. The fix introduces limit readers for all readers that consume data from external sources, preventing unbounded resource consumption during gzip inflation. The patch is available via GitHub Commit 2be3903. Additional details are provided in the GitHub Security Advisory GHSA-6p9p-q6wh-9j89.
Workarounds
- Implement process-level resource limits (cgroups, ulimits) for apko operations
- Pre-validate APK archives for suspicious compression ratios before processing
- Use timeout wrappers around apko build commands to prevent indefinite hangs
- Isolate APK processing in resource-constrained containers or sandboxes
# Configuration example - Set resource limits for apko processes
# Using ulimit to restrict CPU time
ulimit -t 300 # Limit CPU time to 300 seconds
# Using cgroups v2 to limit resources
systemd-run --scope -p CPUQuota=50% -p MemoryMax=2G apko build config.yaml image.tar
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
