CVE-2026-59250
Received Received - Intake

Buffer Overflow in Erlang/OTP Megaco Flex Scanner

Publication date: 2026-07-27

Last updated on: 2026-07-27

Assigner: EEF

Description
Classic buffer overflow in the Erlang/OTP megaco flex scanner C driver allows a remote unauthenticated attacker to corrupt the driver's memory (and potentially achieve remote code execution or a denial-of-service crash) by sending a single text-encoded H.248/Megaco message containing an oversized property parm name. When tokenizing a Local/Remote descriptor, mfs_load_property_groups extracts the attacker-controlled property name (bounded only by the message length) and, when no value follows, formats it into a fixed 512-byte error_msg field of the MfsErlDrvData struct using an unchecked sprintf call. Names longer than roughly 452 bytes overflow into the immediately following struct fields (text_buf, text_ptr, term_spec, term_spec_size, term_spec_index), overwriting live pointers and counters with attacker-chosen bytes. Subsequent scanner code writes and frees through the corrupted pointers, producing arbitrary write and arbitrary free primitives inside the BEAM VM process, which can be leveraged for remote code execution. On builds compiled with _FORTIFY_SOURCE the overflow is detected at runtime and terminates the process with SIGABRT, resulting in denial of service. The overflow occurs in the flex scanner before any grammar or Megaco-level authentication processing, so exploitation requires only network reachability to the megaco transport port on a node configured with {scanner, flex}. This vulnerability is associated with program files lib/megaco/src/flex/megaco_flex_scanner_drv.flex.src and program routines mfs_load_property_groups. This issue affects OTP from OTP 17.0 before OTP 29.0.4, OTP 28.5.0.4 and OTP 27.3.4.15, corresponding to megaco from 3.17.1 before 4.9.1, 4.8.3.1 and 4.7.2.2. Versions prior to OTP 17.0 are also affected but are not listed because the OTP version scheme is only defined from OTP 17.0 onwards.

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Meta Information

Published
2026-07-27
Last Modified
2026-07-27
Generated
2026-07-27
AI Q&A
2026-07-27
EPSS Evaluated
N/A
NVD
CVE-2026-59250
EUVD
EUVD-2026-49324

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
erlang otp From 17.0 (inc) to 29.0.4 (exc)
erlang megaco From 3.17.1 (inc) to 4.9.1 (exc)
erlang megaco to 4.8.3.1 (exc)
erlang megaco to 4.7.2.2 (exc)

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Exploitability

CWE
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KEV
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CWE ID Description
CWE-120 The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer.
CWE-787 The product writes data past the end, or before the beginning, of the intended buffer.

Attack-Flow Graph

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Executive Summary

This is a classic buffer overflow in the Erlang/OTP Megaco flex scanner C driver. A remote unauthenticated attacker can send a specially crafted H.248/Megaco message with an oversized property parameter name. When the scanner processes a Local/Remote descriptor, it copies the attacker-controlled name into a fixed 512-byte error message buffer using an unchecked sprintf call. Names longer than about 452 bytes overflow into adjacent memory fields, corrupting pointers and counters. This can lead to arbitrary write and free operations within the BEAM VM process, potentially enabling remote code execution. On systems with _FORTIFY_SOURCE enabled, the overflow triggers a runtime detection and causes a denial-of-service crash.

The vulnerability occurs before any authentication or protocol-level validation, so exploitation requires only network access to the Megaco transport port on a node configured with the flex scanner.

Detection Guidance

To detect this vulnerability, check if your Erlang/OTP system is running a vulnerable version (OTP 17.0 to 29.0.3, 28.5.0.3, or 27.3.4.14). Inspect the megaco application configuration for {scanner, flex} and verify if the megaco transport port is exposed to the network. Use commands like 'erl -version' to check OTP version and 'netstat -tulnp | grep megaco' to check port exposure.

Impact Analysis

An attacker could exploit this to crash the Erlang node running the Megaco text codec, causing a denial-of-service. Without _FORTIFY_SOURCE protection, the attacker might achieve remote code execution, potentially taking full control of the system. This could lead to data theft, service disruption, or further network compromise.

Compliance Impact

This vulnerability could lead to unauthorized access or data breaches, violating GDPR's integrity and confidentiality requirements or HIPAA's safeguards for protected health information. A successful exploit may result in non-compliance, legal penalties, or reputational damage due to compromised systems handling sensitive data.

Mitigation Strategies

Immediately upgrade to patched versions: OTP 29.0.4, 28.5.0.4, or 27.3.4.15. Alternatively, disable the flex scanner by setting {scanner, erl} in megaco configuration or restrict network access to the megaco transport port. If upgrading is not possible, apply network-level restrictions as a temporary measure.

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