CVE intelligence and bounded remediation

CVE-2020-24034 — Sagemcom F@St 5280 Router Firmware security vulnerability

High CVSS 9

Sagemcom F@ST 5280 routers using firmware version 1.150.61 have insecure deserialization that allows any authenticated user to perform a privilege escalation to any other user. By making a request with valid sess_id, nonce, and ha1 values inside of the serialized session cookie, an attacker may alter the user value inside of this cookie, and assume the role and permissions of the user specified. By assuming the role of the user internal, which is inaccessible to end users by default, the attacker gains the permissions of the internal account, which includes the ability to flash custom firmware to the router, allowing the attacker to achieve a complete compromise.

Severity
High
CVSS
9 (2.0)
Published
2020-09-01
CISA KEV
Not currently listed
Ecosystem
operating-system
Weaknesses
CWE-502

Affected products

  • sagemcom / f@st_5280_router_firmware / 1.150.61

Matched remediation archetype

Unsafe deserialization and object reconstruction

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Check exposure

  • Inventory serialization formats accepted from requests, queues, caches, files, cookies, and cross-service messages.
  • Trace whether untrusted input can select classes, types, callbacks, constructors, or object hooks during decoding.
  • Identify signing, schema validation, trust-boundary, and compatibility settings for each decoder.

Remediate safely

  • Replace native object deserialization with a data-only format and explicit schema validation.
  • If replacement is not immediate, use a safe decoder with a minimal type allowlist and disable polymorphic or executable hooks.
  • Update the affected library and add inert tests for unknown types, extra fields, malformed nesting, and unsigned data.

Authoritative sources

Complete CVE record and remediation plan

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