CVE-2026-87779: Apache Syncope Information Disclosure Flaw

CVE-2026-87779 Overview

Apache Syncope contains an information disclosure vulnerability where cryptographic key material is written to log files. When an administrator configures an Advanced Encryption Standard (AES) key with a non-standard length (not 16, 24, or 32 bytes), Syncope pads the value with random characters and then logs the resulting key. Attackers with access to log files can recover the AES key used to protect sensitive Syncope data.

The vulnerability is tracked as CWE-532: Insertion of Sensitive Information into Log File.

Critical Impact
The AES key that protects sensitive Apache Syncope data is written to logs in plaintext, allowing anyone with log access to decrypt protected values.

Affected Products

Apache Syncope 3.0.15 through 3.0.16
Apache Syncope 4.0.3 through 4.0.7
Apache Syncope 4.1.0-M0 through 4.1.2

Discovery Timeline

2026-09-14 - CVE-2026-87779 published to the National Vulnerability Database (NVD)
2026-09-14 - Last updated in NVD database

Technical Details for CVE-2026-87779

Vulnerability Analysis

Apache Syncope uses an AES symmetric key to encrypt sensitive fields such as credentials and configuration secrets. AES requires a key of exactly 16, 24, or 32 bytes, corresponding to AES-128, AES-192, or AES-256.

When an operator configures a key that does not match one of these lengths, Syncope silently pads the supplied value with random bytes to produce a valid AES key. During this process the derived key is written to the application log at a level that persists to disk.

Any actor able to read the log file, including administrators, backup operators, log aggregation services, or an attacker who reaches log storage, obtains the full encryption key. With the key in hand, an attacker can decrypt every value that Syncope has encrypted with it.

The Exploit Prediction Scoring System (EPSS) rates this issue at 0.413% with a percentile of 35.3, and no public exploit or proof of concept has been observed.

Root Cause

The defect stems from two design choices in Apache Syncope. First, the code accepts and silently normalizes AES keys of invalid length rather than rejecting the configuration. Second, the normalized key material is emitted to a log sink, violating the principle that secrets must never be written to persistent logs. Together, these behaviors turn a lenient input handler into a sensitive information disclosure primitive.

Attack Vector

The vulnerability is network-adjacent in the sense that logs are frequently shipped to centralized systems reachable over the network. An attacker does not exploit Syncope directly. Instead, the attacker reads the log file, extracts the padded AES key, and uses it offline to decrypt any Syncope-encrypted data they can access. Insider misuse, over-permissioned log platforms, and compromised log storage each provide viable paths to the key.

No exploitation code is required. Refer to the Apache mailing list announcement and the OpenWall oss-security post for the vendor's technical description.

Detection Methods for CVE-2026-87779

Indicators of Compromise

Apache Syncope log entries that reference AES key initialization or key padding around the time a non-standard key length was configured.
Log lines containing high-entropy strings adjacent to configuration keywords such as secretKey, AES, or encryption.
Read access to Syncope log files or log aggregation indices from accounts or services that do not require it.

Detection Strategies

Grep archived Syncope logs for the AES key configuration parameter and any nearby literal key values, then treat any match as a compromised key.
Compare currently configured AES key lengths against the allowed values of 16, 24, or 32 bytes to identify Syncope instances that would trigger the padding behavior.
Audit which principals and downstream systems have historical access to Syncope logs, including SIEM indexes, backup snapshots, and developer workstations.

Monitoring Recommendations

Alert on new reads of Syncope log files or log indices by non-operational identities.
Monitor Syncope configuration changes that alter the encryption key or key length.
Track upgrade status across all Syncope deployments until every instance runs a fixed version.

How to Mitigate CVE-2026-87779

Immediate Actions Required

Upgrade Apache Syncope to version 4.0.8 or 4.1.3, which remove the logging of derived AES key material.
Rotate the AES encryption key on every affected Syncope instance and re-encrypt stored secrets with the new key.
Purge historical Syncope logs that may contain the padded AES key from all systems, including SIEM, backups, and log archives.
Rotate any credentials or secrets that Syncope encrypted with the exposed key, since offline decryption remains possible for anyone who copied the logs.

Patch Information

The Apache Syncope project fixed the issue in versions 4.0.8 and 4.1.3. Users on the 3.0.x branch should plan migration, as fixes are published for the 4.0 and 4.1 branches. Full details are available in the Apache mailing list thread.

Workarounds

Configure the AES key with a length of exactly 16, 24, or 32 bytes so that Syncope does not enter the padding code path.
Restrict read access to Syncope log files and downstream log stores to a minimal set of operational accounts.
Route Syncope logs through a filter that redacts high-entropy values near known key-related log messages until the patch is applied.

bash

# Example: generate a compliant 32-byte (AES-256) key and check its length
openssl rand -base64 32 > syncope-aes.key
wc -c < <(openssl rand 32)   # must report 32