CVE-2026-78242: Apache APISIX Information Disclosure Flaw

CVE-2026-78242 Overview

CVE-2026-78242 is an information disclosure vulnerability in Apache APISIX, an open-source API gateway. The flaw [CWE-532] causes unmasked HTTP header values to be written to log sinks under certain response structures. Sensitive data intended to be masked—such as authorization tokens, API keys, or session identifiers—can be exposed in log files accessible to local users or downstream log aggregation systems. The issue affects Apache APISIX 3.17.0, and the project maintainers have released version 3.18.0 to address it.

Critical Impact
Sensitive HTTP header values can leak into log sinks in cleartext, exposing credentials and tokens to anyone with access to log storage or forwarding pipelines.

Affected Products

Apache APISIX 3.17.0
Deployments using header masking configurations in log plugins
Downstream SIEM or log aggregation systems ingesting APISIX logs

Discovery Timeline

2026-10-01 - CVE CVE-2026-78242 published to NVD
2026-10-01 - Last updated in NVD database

Technical Details for CVE-2026-78242

Vulnerability Analysis

The vulnerability resides in Apache APISIX's logging subsystem, where response headers that should be masked before being written to log sinks are instead recorded in their original form. The flaw triggers only under specific response structures, meaning the exposure depends on how upstream services shape their responses. When the condition is met, the gateway bypasses the masking logic and sends the raw header value to the configured log destination. This maps to [CWE-532] Insertion of Sensitive Information into Log File.

The attack requires local access and low privileges, with no user interaction, and impacts confidentiality only. Integrity and availability of the gateway are not affected. The exposure extends to any system that consumes APISIX logs, including file-based sinks, Kafka, Elasticsearch, and remote syslog targets.

Root Cause

The root cause is a conditional path in the response-handling pipeline where header masking is skipped for particular response structures. Instead of applying the masking filter uniformly, the logger writes the unmasked header value directly to the sink. Sensitive values such as Authorization, Cookie, or custom tokens are preserved verbatim.

Attack Vector

An attacker with access to the log destination can harvest credentials, tokens, or personal data from the recorded entries. The attack vector is local because an adversary must read the log sink to recover the data. In environments where logs are forwarded to shared observability platforms, the exposure can extend to anyone with query access to those platforms.

See the Apache Mailing List Thread and the OpenWall OSS-Security Update for upstream technical details.

Detection Methods for CVE-2026-78242

Indicators of Compromise

Log entries from APISIX 3.17.0 containing cleartext values in headers that are configured to be masked, such as Authorization: Bearer ... or Cookie: session=....
Unexpected credential strings appearing in log aggregation platforms sourced from the gateway.
Access patterns showing unprivileged accounts reading APISIX log files or querying log indices for header fields.

Detection Strategies

Audit existing APISIX log archives for the presence of header values that should have been redacted, using regular expressions targeting token formats.
Correlate log-reader activity with log file paths used by APISIX to identify accounts accessing exposed logs.
Review log pipeline configurations to identify sinks that have retained unmasked payloads from the affected version.

Monitoring Recommendations

Alert on new log entries containing patterns consistent with bearer tokens, JWTs, or API keys from APISIX log sources.
Monitor access to log storage, SIEM indices, and object storage buckets receiving gateway logs.
Track upgrades of APISIX across the fleet to confirm no instances remain on 3.17.0.

How to Mitigate CVE-2026-78242

Immediate Actions Required

Upgrade Apache APISIX from 3.17.0 to 3.18.0 or later, which contains the fix.
Rotate any credentials, API keys, or session tokens that may have been recorded in logs while running the affected version.
Restrict read access to APISIX log files, sinks, and downstream aggregation indices to least-privilege accounts.
Purge or re-redact historical log data that may contain exposed header values.

Patch Information

The Apache APISIX project has released version 3.18.0 to resolve CVE-2026-78242. The patch restores masking of header values across the affected response structures. Refer to the Apache Mailing List Thread and the OpenWall OSS-Security Update for the official release notice.

Workarounds

If an immediate upgrade is not possible, disable or reconfigure log plugins that record response headers until the patch is applied.
Apply additional post-processing redaction in the log pipeline to strip sensitive header fields before storage.
Isolate the log sink on access-controlled storage with encryption at rest to reduce exposure of any residual sensitive data.

bash

# Upgrade Apache APISIX to the fixed release
# Verify current version
apisix version

# Example: upgrade via package manager (Debian/Ubuntu)
sudo apt-get update
sudo apt-get install --only-upgrade apisix=3.18.0

# Example: upgrade via Helm
helm upgrade apisix apisix/apisix --version 3.18.0 -n ingress-apisix

# Confirm the new version is active
apisix version