jsrsasign: Division by Zero Allows Invalid JWK Modulus to Cause Deterministic Zero Output in RSA Operations

published 2026-03-23 7 mo ago modified 2026-06-22 4 mo ago also GHSA-464q-cqxq-xhgr , EUVD-2026-14380

cvss: 5.9; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.1%; EPSS 0.1% chance of exploitation in 30 days, percentile 0%
public exploits: 0; none known

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.

Patch / fix

fixed in 2 links 2

npm jsrsasign 11.1.1
n/a jsrsasign 11.1.1

github.com/kjur/jsrsasign@dc41d49 commit
github.com/kjur/jsrsasign#649 pull request

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-4603 updated 2026-06-28 cvss 5.9

jsrsasign: jsrsasign: Cryptographic operations impacted by division by zero via malicious JSON Web Key

Red Hat Migration Toolkit for Virtualization mtv-candidate/mtv-console-plugin-rhel9, migration-toolkit-virtualization/mtv-console-plugin-rhel9 Red Hat Quay 3 quay/quay-rhel8, quay/quay-rhel9
affected: workaround, no fix available “Fix deferred”

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: 7 mo ago (2026-03-23)

Exploit prediction

0.10% chance of exploitation in the next 30 days, higher than 0% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

gist.github.com https://gist.github.com/Kr0emer/5366b7364c4fbf7e754bc377f321e9f3 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	4.0	5.1	CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:P
CNA	3.1	5.9	CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L/E:P
CNA	4.0	2.0	CVSS:4.0/AV:L/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CNA	3.1	5.9	CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L
NVD	3.1	5.3	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:L
GitHub	3.1	5.9	CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:L

Affected packages

ecosystem	package	affected	fixed in
npm	jsrsasign	<11.1.1	11.1.1

Affected products

n/a jsrsasign

Classification

Weakness

CWE-369 Divide By Zero

References

github.com /kjur/jsrsasign/commit/dc41d49fac4297e7a737a3ef8ebd0aa9c49ef93f
web, patch
github.com /kjur/jsrsasign/pull/649
web, issue-tracking
gist.github.com /Kr0emer/5366b7364c4fbf7e754bc377f321e9f3
web, exploit, mitigation, third-party-advisory
security.snyk.io /vuln/SNYK-JS-JSRSASIGN-15371176
web, third-party-advisory
nvd.nist.gov /vuln/detail/CVE-2026-4603
advisory
github.com /kjur/jsrsasign
package

Sources

CVE List CVE-2026-4603
GitHub Advisory GHSA-464q-cqxq-xhgr
NVD CVE-2026-4603

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary