CVE-2026-59296 Overview
CVE-2026-59296 affects Micrometer, the application observability facade used by Spring and other Java frameworks. The vulnerability allows attackers to inject arbitrary content into metrics data when applications pass untrusted, non-normalized input as metric names, tag keys, or tag values. This antipattern enables adversaries to corrupt telemetry pipelines, poison dashboards, and manipulate monitoring integrity. The issue is classified under [CWE-74] (Improper Neutralization of Special Elements in Output).
Critical Impact
Attackers with network access can inject malicious content into metrics streams, compromising the integrity of observability data used for operational and security decisions.
Affected Products
- Micrometer 1.17.0
- Micrometer 1.16.0 through 1.16.6, 1.15.0 through 1.15.12, and 1.14.0 through 1.14.16
- Micrometer 1.9.18 and earlier
Discovery Timeline
- 2026-08-21 - CVE-2026-59296 published to the National Vulnerability Database
- 2026-08-27 - Last updated in NVD database
Technical Details for CVE-2026-59296
Vulnerability Analysis
Micrometer provides a vendor-neutral instrumentation facade for collecting application metrics. The library forwards metric names, tag keys, and tag values to downstream backends such as Prometheus, Datadog, or StatsD. When application code passes untrusted user input directly into these fields without normalization, the input is emitted as-is into the metrics pipeline.
An attacker who controls values reflected into metrics can inject delimiter characters, newlines, or backend-specific control sequences. The result is telemetry poisoning: malformed exposition output, cardinality explosions, or forged metric series that mislead monitoring and alerting systems. High attack complexity applies because exploitation depends on the target application exposing user-controlled paths into instrumentation calls.
Root Cause
Micrometer historically emitted caller-supplied strings without enforcing a normalization contract. The library trusted the calling application to sanitize inputs before passing them to Meter identifiers or Tag values. When applications violated that expectation, downstream serializers reproduced the raw bytes, breaking backend parsers or creating unbounded label sets.
Attack Vector
Exploitation requires an application path that instruments a metric using attacker-controlled input. Common patterns include tagging metrics with HTTP header values, request paths, or query parameters. The attacker submits crafted values containing backend-specific separators or high-cardinality tokens to disrupt the metrics stream over the network. No authentication or user interaction is required against a vulnerable instrumentation surface. Refer to the Spring Security Advisory CVE-2026-59296 for backend-specific injection details.
Detection Methods for CVE-2026-59296
Indicators of Compromise
- Unexpected metric names or tag values containing newline, comma, or pipe characters in exposition endpoints such as /actuator/prometheus.
- Rapid growth in time-series cardinality tied to a single meter identifier.
- Parser errors or dropped samples reported by downstream metrics backends.
Detection Strategies
- Audit application code for calls to Metrics.counter, Timer.builder, and Tags.of that accept request-derived strings without sanitization.
- Enable Micrometer meter filters that reject or transform meters with invalid characters and log rejections for review.
- Compare emitted metric schemas against an allowlist of expected names and tag keys during CI validation.
Monitoring Recommendations
- Alert on sudden cardinality spikes per meter using backend-native monitoring such as Prometheus prometheus_tsdb_symbol_table_size_bytes.
- Ingest application and metrics-scraper logs into a centralized data lake for correlation with request telemetry.
- Track Micrometer library versions across services and flag hosts running affected releases.
How to Mitigate CVE-2026-59296
Immediate Actions Required
- Upgrade Micrometer to a patched release aligned with the version tracks listed in the Spring advisory.
- Inventory application code paths that pass HTTP inputs, headers, or user identifiers into metric names or tags and remove those flows.
- Deploy a global MeterFilter that normalizes or denies unexpected characters before meters reach the registry.
Patch Information
Upgrade to the patched Micrometer versions referenced in the Spring Security Advisory CVE-2026-59296. Applications on Micrometer 1.9.x should migrate to a supported branch, since older releases remain out of maintenance.
Workarounds
- Wrap instrumentation calls in a helper that applies strict allowlist validation to metric identifiers and tag values.
- Register a MeterFilter.denyUnless policy that permits only known meter names.
- Terminate metrics scraping endpoints behind authenticated internal networks to reduce exposure while patching.
# Configuration example
# See the Spring Security Advisory for vendor-specific remediation guidance.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
