Home/CVE/JWT is a library to work with JSON Web Token and JSON Web Signature. Prior to versions 3.4.6, 4.0.4, and 4.1.5, users of
CVE
CVE-2021-41106
JWT is a library to work with JSON Web Token and JSON Web Signature. Prior to versions 3.4.6, 4.0.4, and 4.1.5, users of
JWT is a library to work with JSON Web Token and JSON Web Signature. Prior to versions 3.4.6, 4.0.4, and 4.1.5, users of HMAC-based algorithms (HS256, HS384, and HS512) combined with Lcobucci\JWT\Signer\Key\LocalFileReference as key are having their tokens issued/validated using the file path as hashing key - instead of the contents. The HMAC hashing functions take any string as input and, since users can issue and validate tokens, users are lead to believe that everything works properly.
Versions 3.4.6, 4.0.4, and 4.1.5 have been patched to always load the file contents, deprecated the Lcobucci\JWT\Signer\Key\LocalFileReference, and suggest Lcobucci\JWT\Signer\Key\InMemory as the alternative. As a workaround, use Lcobucci\JWT\Signer\Key\InMemory instead of Lcobucci\JWT\Signer\Key\LocalFileReference to create the instances of one's keys.
MEDIUM · CVSS 4.4
EPSS 0.00034
Schedule remediation
- Public exploit or PoC is available
Sigma rules0
YARA rules0
Look this up elsewhere - one-click external pivots
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How to read a CVE - triage first, then detect and patch
This page is every public fact about CVE-2021-41106, cross-linked. Its job is to answer one question fast - does this need my attention now? - and then hand you the two things you do about it. Here is how an analyst reads it.
Triage: should I act now? Four signals, and they are not interchangeable:
CVSSseverity - how bad it is IF exploited, 0-10. A high CVSS alone is not urgency; a flaw can be a perfect 10 and never actually be attacked.
EPSSprobability - a model’s estimate of the chance it is exploited in the next 30 days, 0-1. This is the “will it actually happen” signal.
CISA KEVconfirmed - it is being exploited in the wild right now. The strongest signal on the page; KEV beats any score.
Weaponisedavailability - public exploits / PoCs, and especially Metasploit modules rated Excellent / Great. Reliable, packaged exploit code means low-skill attackers can use it today.
How they combine: KEV, or a dependable Metasploit module, means patch now regardless of CVSS. High CVSS + low EPSS + no exploit is real but not an emergency - schedule it. Low CVSS but KEV-listed still gets patched now. The verdict above already weighed these for you; this is how it got there.
Then what - two workflows:
Detectwhen you cannot patch today, follow this CVE to the ATT&CK techniques it enables, then Build a SIEM detection (the green button) - author a rule, test it in Atomic, deploy it. That buys visibility while the patch waits.
PatchAffected products / packages tell you if you are exposed; Fixed versions by distribution and Vendor advisories give the exact version that closes it.
Reading order for the panels below: verdict + badges, then Public exploits / Metasploit (is it weaponised), then ATT&CK techniques + Sigma / IDS rules (can I detect it), then Affected products / packages + Fixed versions (am I exposed, what patches it), then Threat actors / IOCs (who uses it), then Scoring & timeline / references (the evidence).
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ATT&CK techniques
6Techniques this CVE enables - linked via CWECAPECATT&CK. High◆ = named directly in ATT&CK or Nuclei templates.
T1211 · Exploitation for Stealth T1491 · Defacement T1542.002 · Component Firmware T1556 · Modify Authentication Process T1557.002 · ARP Cache Poisoning T1584.002 · DNS Server
▤ Build a SIEM detection for these techniques
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CAPEC attack patterns
12Attack patterns this CVE enables - the bridge from weakness to ATT&CK technique.
CAPEC-CAPEC-111 · JSON Hijacking (aka JavaScript Hijacking) CAPEC-CAPEC-141 · Cache Poisoning CAPEC-CAPEC-142 · DNS Cache Poisoning CAPEC-CAPEC-148 · Content Spoofing CAPEC-CAPEC-218 · Spoofing of UDDI/ebXML Messages CAPEC-CAPEC-384 · Application API Message Manipulation via Man-in-the-Middle CAPEC-CAPEC-385 · Transaction or Event Tampering via Application API Manipulation CAPEC-CAPEC-386 · Application API Navigation Remapping CAPEC-CAPEC-387 · Navigation Remapping To Propagate Malicious Content CAPEC-CAPEC-388 · Application API Button Hijacking CAPEC-CAPEC-665 · Exploitation of Thunderbolt Protection Flaws CAPEC-CAPEC-701 · Browser in the Middle (BiTM)
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Weakness Classification
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Affected Products & Versions
3▤
Affected Packages
1Language-ecosystem packages (from OSV) tied to this CVE, with the version that fixes it - the dependency-level detail NVD doesn’t carry.
Packagist
lcobucci/jwt
MEDIUM
fixed in 3.4.6
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Public Exploits & PoCs
1These PoC and exploit links come from public sources and are not verified to be safe or functional. Review the code before running anything, and treat unverified entries as untrusted.
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Scoring & Timeline
4.4
MEDIUM · CVSS v3.1 · [email protected]
Attack Vector
Network
Adjacent
Local
Physical
Attack Complexity
Low
High
Privileges Required
None
Low
High
User Interaction
None
Required
Scope
Unchanged
Changed
Confidentiality
None
Low
High
Integrity
None
Low
High
Availability
None
Low
High
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References & Sources
3Source URLs (vendor pages, mailing lists, write-ups). Exploit/PoC links are in their own section above to avoid duplication.
https://github.com/lcobucci/jwt/commit/8175de5b841fbe3fd97d2d49b3fc15c4ecb39a73PatchThird Party Advisory
https://github.com/lcobucci/jwt/commit/c45bb8b961a8e742d8f6b88ef5ff1bd5cca5d01cPatchThird Party Advisory