CVE Intelligence
Medium exploit reference

CVE-2026-4603 — Versions of the package jsrsasign before 11.1.1 are vulnerable to Division by zero due…

Versions of the package jsrsasign before 11.1.1 are vulnerable to Division by zero due to the RSASetPublic/KEYUTIL parsing path in ext/rsa.js and the BigInteger.modPowInt reduction logic in ext/jsbn.js. An attacker can force RSA public-key operations (e.g., verify and encryption) to collapse to deterministic zero outputs and hide “invalid key” errors by supplying a JWK whose modulus decodes to zero.

Published Mar 23, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: snyk

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 0.1% (30-day exploitation probability)+0
  • Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
0.11%
ahead of 1% of scored CVEs · Oct 14, 2026
Affects
Kjur
Jsrsasign
CVSS base
5.3
Medium · 3 source(s)
Prioritization reference: 5.9 provisional

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
None
none · proof-of-concept · active
Automatable
No
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

  • Documented mitigation — gist.github.com (NIST National Vulnerability Database)
  • Documented patch — github.com (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Kjur Jsrsasign).
  2. Apply the fixed version or the patch documented under Remediation.
  3. Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Kjur Jsrsasign < 11.1.1 Vulnerable NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
Low

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
5.1 CVSS 4.0 Medium — — snyk via CVE Program (cve.org) e CISA ADP
2.0 CVSS 4.0 Low — — report@snyk.io via NIST National Vulnerability Database
5.9 CVSS 3.1 Medium 2.5 3.4 report@snyk.io via NIST National Vulnerability Database
5.9 CVSS 3.1 Medium — — snyk via CVE Program (cve.org) e CISA ADP
5.3 CVSS 3.1 Medium 1.8 3.4 nvd@nist.gov via NIST National Vulnerability Database
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L (score shown at the top: nvd@nist.gov)
Scoring entities (NIST, CNA, ADP) score independently; each score is shown with its origin. For prioritization we use 5.9 (report@snyk.io via NIST National Vulnerability Database) as a conservative provisional reference — not a definitive official score.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-369

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.11%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
endpoint telemetry (EDR)

Timeline

What happened to this CVE, newest first.

  • 2026
  • SSVC assessment updated
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 13, 2026
  • Fix documented
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVSS changed · 5.3
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · → Analyzed
    Oct 13, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVE published
    Mar 23, 2026 · snyk

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

4 on the record

Elsewhere on this site

Kjur
every CVE for this vendor
CWE-369
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-4602 Versions of the package jsrsasign before 11.1.1 are vulnerable to Incorrect Conversion… Mar 23, 2026
  • CVE-2026-4598 Infinite Loop in Kjur Jsrsasign Mar 23, 2026
  • CVE-2026-4599 Versions of the package jsrsasign from 7.0.0 and before 11.1.1 are vulnerable to… Mar 23, 2026
  • CVE-2026-4600 Improper Verification of Cryptographic Signature in Kjur Jsrsasign Mar 23, 2026
  • CVE-2026-4601 Versions of the package jsrsasign before 11.1.1 are vulnerable to Missing Cryptographic… Mar 23, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-4603 is "Versions of the package jsrsasign before 11.1.1 are vulnerable to Division by zero due…", rated Medium. It affects Jsrsasign (Kjur); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.3 describes technical severity. EPSS 0.11% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

Comments

Moderated technical discussion. Read the community guidelines.

No comments yet.

Sign in or create an account to comment and suggest corrections.