CVE-2025-0695 Overview
CVE-2025-0695 is a resource exhaustion vulnerability in Cesanta Frozen, a JSON parser library used in embedded systems and IoT applications. Versions prior to 1.7 fail to enforce limits on resource allocation when parsing JSON input. An attacker can supply a maliciously crafted JSON payload to trigger a crash in the application embedding the library. The flaw is tracked under CWE-770: Allocation of Resources Without Limits or Throttling. The vulnerability affects availability but does not impact confidentiality or integrity.
Critical Impact
Remote attackers can crash any application embedding vulnerable versions of the Cesanta Frozen JSON parser by sending crafted JSON input, resulting in denial of service.
Affected Products
- Cesanta Frozen JSON parser library versions less than 1.7
- Embedded systems and IoT firmware bundling vulnerable Frozen releases
- Applications and services that expose JSON parsing surfaces through Frozen
Discovery Timeline
- 2025-01-27 - CVE-2025-0695 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-0695
Vulnerability Analysis
Cesanta Frozen is a lightweight JSON parser written in C, commonly embedded in resource-constrained devices. The library processes JSON input without enforcing bounds on nested structures or allocation depth. When a caller feeds attacker-controlled JSON into the parser, the parsing routine consumes resources proportional to the structural complexity of the input.
A crafted document with deeply nested arrays or objects drives the parser into an unbounded state. This exhausts stack or heap resources and terminates the embedding process. The vulnerability is categorized as a denial of service resulting from missing input throttling controls.
Root Cause
The root cause is the absence of depth or resource limits in the Frozen parsing logic. [CWE-770] describes software that allocates a reusable resource without enforcing quotas. Frozen versions prior to 1.7 do not cap recursion depth, object counts, or memory allocation during parse operations. Malformed but structurally valid JSON therefore forces the parser to allocate until the host process fails.
Attack Vector
Exploitation requires network reachability to an endpoint that forwards JSON input into the vulnerable Frozen library. The attacker sends a crafted JSON payload — typically featuring deep nesting or repeated structural tokens — to that endpoint. No authentication or user interaction is required. The affected component crashes, breaking service availability for legitimate clients. Refer to the Nozomi Networks Vulnerability Advisory for the full technical analysis and proof-of-concept details.
Detection Methods for CVE-2025-0695
Indicators of Compromise
- Unexpected crashes or restarts of services or firmware components that parse JSON input from network sources
- Inbound JSON payloads containing unusually deep nesting of arrays or objects, or abnormally large structural token counts
- Repeated malformed JSON requests originating from a single source targeting the same endpoint
Detection Strategies
- Inspect application and system logs for segmentation faults, out-of-memory errors, or process termination events tied to JSON-handling components
- Deploy web application firewall or API gateway rules that reject JSON payloads exceeding a defined nesting depth or byte size
- Correlate crash telemetry with recent inbound requests to identify malformed JSON documents as the trigger
Monitoring Recommendations
- Track process availability and restart counts for services embedding Frozen or similar C-based JSON parsers
- Alert on spikes in 5xx responses or connection resets from JSON API endpoints
- Monitor memory and CPU consumption of embedded devices for anomalous allocation patterns during JSON handling
How to Mitigate CVE-2025-0695
Immediate Actions Required
- Inventory all applications, firmware images, and containers that link against the Cesanta Frozen library
- Upgrade Cesanta Frozen to version 1.7 or later where the allocation limits are enforced
- Restrict network exposure of JSON parsing endpoints to trusted callers until upgrades are complete
Patch Information
Upgrade to Cesanta Frozen version 1.7 or later. Rebuild and redistribute any firmware or applications that statically link the library. Consult the Nozomi Networks Vulnerability Advisory for upstream fix references and downstream impact guidance.
Workarounds
- Place a reverse proxy or API gateway in front of vulnerable services to enforce maximum JSON size and nesting depth
- Validate and pre-parse JSON input with a hardened parser before handing structured data to Frozen-based components
- Apply rate limiting and connection throttling on JSON endpoints to reduce the blast radius of repeated crash attempts
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
