External risk intelligence

Libtasn1 Encoding Vulnerability Affects ASN.1 Structures

CVE advisorySeverity: CRITICAL (CVSS 9.1)

CVE-2021-46848

GNU Libtasn1 is a foundational library used for ASN.1 structure handling, often within cryptographic and protocol implementations. While it is not a standalone internet-facing service, it is frequently embedded in network-accessible applications and security protocols that process external data, making reachability possible in various deployments, though it lacks a singular common public-facing deployment pattern.

Gnu Libtasn1

before 4.19.035363710.0

Halo Surface Signal: 3 out of 5 — possibly public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A critical vulnerability has been identified in GNU Libtasn1, a library used for handling ASN.1 data structures. This issue could potentially allow for significant data compromise or denial of service when processing malformed data. While direct exploitation might be complex, its presence in foundational security components means its impact could be widespread across various applications and systems. The main concern is confirming relevance and exposure.

A flaw exists in a common data processing library.
It impacts security functions and data integrity.
Confirm relevance and exposure across systems.

Attack Path

How an attacker could exploit the issue

An attacker could reach this vulnerability by sending specially crafted data over the network to an application that uses the vulnerable component. This data would be processed by the `asn1_encode_simple_der` function, triggering an off-by-one error in an array size check. Success could allow an attacker to impact the confidentiality and availability of the affected system.

Requires no authentication or privileges.
Triggered by processing malformed input.
Risk to confidentiality and availability.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could impact systems that process ASN.1 data using GNU Libtasn1, potentially leading to service instability or denial of service when handling malformed input. The core issue lies in an off-by-one error during DER encoding, which, when triggered, can cause unexpected behavior in applications relying on this library for structured data processing.

Affected: System data processing integrity.
Exposure: Malformed ASN.1 data input.
Consequence: Service instability or denial of service.

Operational Fix

Recommended remediation, mitigation, and detection steps

The GNU Libtasn1 library's vulnerability is likely to be addressed by teams managing applications that incorporate this library, potentially platform or development teams, in coordination with infrastructure and security operations. The initial practical move is to identify where Libtasn1 is deployed, assess its exposure and criticality, and then plan remediation, possibly involving vendor coordination or temporary risk reduction measures if immediate patching is not feasible.

Application owners and platform teams should lead.
Verify affected application exposure and criticality.
Plan coordinated remediation within maintenance windows.

Supplementary metadata

CVSS vector

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Frequently asked questions

What is GNU Libtasn1 used for?

GNU Libtasn1 is a foundational C library designed to manage ASN.1 structures. Developers use it to encode and decode data according to ASN.1 standards, which are critical for cryptographic operations, digital certificates, and various network communication protocols that require structured data formats.

What is the vulnerability in CVE-2021-46848?

This vulnerability is an off-by-one error classified as CWE-193. It occurs within an array size check during the ASN.1 encoding process. Specifically, when the library's asn1_encode_simple_der function processes data, the logic error can lead to memory handling issues, potentially impacting data confidentiality or causing the application to crash.

How is this vulnerability triggered?

The flaw is triggered when an application utilizing the library processes specially crafted, malformed input data. It is not triggered by standard, well-formed ASN.1 traffic. The attacker does not need authentication to deliver this data to an application that relies on the vulnerable function.

Why should I care about this vulnerability?

Halo Surface Signal notes that while Libtasn1 is a library rather than a standalone service, it is often embedded in network-accessible applications. If an application using this library accepts input from external sources, it may be reachable by attackers. You should care if your systems handle untrusted network traffic that relies on these ASN.1 structures.

How do I respond to this threat?

Start by identifying which applications and services in your environment incorporate the affected versions of the Libtasn1 library. Once mapped, coordinate with your platform and development teams to prioritize updates. Since this is a shared library, remediation usually involves updating the underlying system packages or recompiling dependent applications to include the fixed version.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.