What Is Deserialization Function? Definition & Examples

A Deserialization Function is code that converts stored or transmitted data back into an in-memory object or structure. If it accepts untrusted input, attackers may trigger object injection, resource exhaustion, or unsafe method calls. Defenders should validate input, restrict allowed types, and avoid deserialising untrusted data where possible.

What a deserialization function does

A deserialization function reverses a prior encoding step, turning stored or transmitted data into an in-memory object, structure, or runtime value that application code can work with.

That sounds routine, but the function is often a trust boundary. If the input is attacker-controlled, the parser may create objects the developer did not intend, trigger application logic during object construction, or allocate more memory and CPU than expected.

Why untrusted deserialization is dangerous

The main security problem is that deserialization can do more than rebuild data. In some languages and libraries, it can invoke methods, resolve class names, or hydrate object graphs in ways that expose unexpected behaviour. That makes it a common route to object injection, unsafe method calls, and denial of service through oversized or deeply nested payloads.

For web applications, this sits in the same family of input-handling flaws as other injection problems. NHIMG’s Web Application Attacks Guide covers insecure deserialisation alongside related attack patterns such as command injection, SSRF, and request smuggling, which helps place the risk in the broader application-attack landscape.

Common failure conditions and exposure paths

Deserialization becomes risky when applications accept serialized data from users, partners, queues, APIs, browser state, or other external systems without strict validation. The exposure is not limited to public endpoints. Internal services can also be vulnerable if they trust messages that were never authenticated, signed, or type-checked before being processed.

Another common failure mode is assuming that “known format” means “safe format.” Binary serialization, JSON wrappers, XML-based object mapping, and framework-specific session blobs can all become hazardous when the receiving code trusts type metadata, embedded references, or object constructors more than the actual business data.

Defenders should treat this as an input-safety and trust-boundary issue, not just a coding convenience. NIST’s Cybersecurity Framework 2.0 provides the broader identify-protect-detect-respond-recover structure for managing software exposure, while NIST SP 800-53 Rev 5 Security and Privacy Controls gives control language for configuration management, system integrity, and input-related safeguards.

Safer design and defensive handling

The safest pattern is to avoid deserializing untrusted data where possible. When deserialization is unavoidable, the application should constrain the accepted types, reject unexpected object graphs, and validate the message before any business logic depends on it. That reduces the chance that parsing itself becomes an execution path.

Practically, this means preferring simple data transfer formats and explicit schema validation over opaque object reconstruction, especially for cross-service communication. It also means reviewing framework defaults, because many deserialization flaws emerge from convenience features that were meant for trusted internal use but later became exposed to untrusted input.

For teams hardening application and service interfaces, the OWASP API Security Top 10 is useful context for broken authentication, broken authorization, and unsafe consumption patterns that often accompany deserialization mistakes in API-driven systems.

Detection and post-incident review

Deserialization abuse often leaves indirect traces rather than a single obvious signature. Useful signals include unusual error bursts, type-resolution failures, recursion or heap spikes, malformed serialized blobs, and requests that trigger unexpected server-side behaviour during parsing. In mature environments, those signals should be correlated with application logs, request metadata, and process telemetry.

If exploitation is suspected, the review should cover whether the payload reached any code path that could instantiate privileged objects, call dangerous methods, or access secrets and sessions in memory. That matters because compromise may not stop at code execution or denial of service, it can also expose credentials, tokens, or application state that the process already held.

MITRE ATT&CK’s Enterprise Matrix is a useful companion for mapping the downstream attacker behaviours that can follow initial exploitation, including privilege escalation, credential access, and lateral movement.

Standards & Framework Alignment

This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.

OWASP API Security Top 10 addresses the attack and risk surface, while NIST CSF 2.0, NIST SP 800-53 Rev 5 and OWASP ASVS set the governance and control requirements practitioners need to meet.

Framework	Control / Reference	Relevance
NIST CSF 2.0	PR.DS-10 — Data-in-Transit is Protected	Deserialization inputs often travel between services and must be protected in transit.
Recommendation — Protect serialized payloads in transit and reject tampered messages before parsing.
NIST SP 800-53 Rev 5	SI-10 — Information Input Validation	Deserialization is an input-validation boundary where untrusted data can trigger unsafe parsing.
	SI-7 — Software, Firmware, and Information Integrity	Unsafe deserialization can compromise application integrity through object injection or hostile logic paths.
Recommendation — Validate serialized input before deserializing it and block unexpected structures or types. Apply integrity checks and trusted-source controls to serialized data before it is processed.
OWASP ASVS	V1 — Encoding and Sanitization	Deserialization safety depends on rejecting malformed or malicious input before object reconstruction.
Recommendation — Sanitize and constrain untrusted serialized data before it reaches object creation logic.
OWASP API Security Top 10	API8 — Security Misconfiguration	Unsafe serializer defaults and permissive type handling are common API misconfiguration issues.
Recommendation — Harden serialization defaults and remove unsafe deserialization settings from exposed APIs.

Deserialization Function