External risk intelligence

jsrsasign Incomplete Comparison Key Recovery Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.3)

CVE-2026-4599

jsrsasign is a cryptographic software library used by developers as a dependency within applications. It does not provide a network-accessible service or interface, and its functions are invoked internally by the host application's code, not directly from the internet.

Kjur Jsrsasign

7.0.0 to before 11.1.1

Halo Surface Signal: 1 out of 5 — much less likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A critical vulnerability exists in the jsrsasign package, a cryptographic library that could allow attackers to recover private keys by exploiting flaws in how it handles comparisons during signature generation. This type of flaw can undermine the security of digital identities and sensitive data.

Flaw in a code library could expose private keys.
Key management and digital signature security are at risk.
Confirm relevance and assess exposure to this library.

Attack Path

How an attacker could exploit the issue

An attacker could exploit this vulnerability by triggering specific functions within the jsrsasign library that are used for generating cryptographic nonces. By providing carefully crafted inputs that bypass incomplete comparison checks, an attacker could bias the random number generation, ultimately leading to the recovery of a private key. This could enable the attacker to impersonate legitimate users or decrypt sensitive information.

No authentication or special access required.
Triggered via specific library functions.
Enables private key recovery.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an attacker to recover private keys when DSA signatures are generated. This is possible due to incorrect comparison checks in the affected functions that can bias the generation of nonces.

Private keys could be compromised.
Attacker exploits improper comparisons.
Compromised keys enable further attacks.

Operational Fix

Recommended remediation, mitigation, and detection steps

The jsrsasign package's cryptographic functions are utilized within applications, meaning application owners or the teams responsible for those applications should lead the investigation. The first practical step is to identify all instances of this library, determine their business criticality and external reachability, and then assign ownership for remediation planning based on the risk assessment.

Confirm application ownership and library usage.
Verify external exposure and business impact.
Plan remediation with affected application teams.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is the jsrsasign library?

jsrsasign is a JavaScript cryptographic library used by developers to implement digital signatures, message authentication, and certificate management within their software. Because it serves as a foundational building block for handling security operations, it is frequently included as a dependency in Node.js applications that require robust cryptographic processing.

How does CVE-2026-4599 work?

This vulnerability involves an 'Incomplete Comparison' weakness (CWE-1023). The library incorrectly handles checks when selecting random numbers for cryptographic nonces during DSA signature generation. Because the library fails to properly exclude out-of-range candidates, the resulting numbers become predictable. If an attacker observes enough signatures, they can leverage this bias to mathematically recover the underlying private key.

What triggers this vulnerability?

The flaw is triggered when an application calls the getRandomBigIntegerZeroToMax or getRandomBigIntegerMinToMax functions within the affected versions. If these functions are used in a process that generates DSA signatures, the predictable nonce generation occurs. It is important to note that the vulnerability is tied to these specific mathematical functions; simply having the library installed without executing these functions for signature signing does not trigger the flaw.

Do I need to worry if my application is internal?

Halo Surface Signal notes that jsrsasign is an internal library rather than an internet-facing service, so it is rarely exposed directly to the internet. However, internal applications using this library to sign sensitive data or authenticate users remain at risk if the application itself processes untrusted input that influences these cryptographic functions. Risk depends on whether the code path is reachable by an attacker, regardless of the application's network perimeter.

How do I address CVE-2026-4599?

Begin by auditing your application inventory to identify which projects rely on the affected jsrsasign versions. Once you locate the dependencies, determine if those applications utilize the vulnerable signature generation functions. Prioritize remediation by updating the package to version 11.1.1 or later. Coordinate with the application development teams to ensure the update is integrated and that any keys potentially exposed while using the vulnerable version are rotated.

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.