CVE Intelligence
Critical File handling exploit reference

CVE-2021-21346 — XStream is vulnerable to an Arbitrary Code Execution attack

XStream is a Java library to serialize objects to XML and back again. In XStream before version 1.4.16, there is a vulnerability which may allow a remote attacker to load and execute arbitrary code from a remote host only by manipulating the processed input stream. No user is affected, who followed the recommendation to setup XStream's security framework with a whitelist limited to the minimal required types. If you rely on XStream's default blacklist of the Security Framework, you will have to use at least version 1.4.16.

Published Mar 22, 2021 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: GitHub_M

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 76.4% (30-day exploitation probability)+15
  • Technical severity (critical)+10
  • Automatable exploitation (SSVC)+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
76.37%
ahead of 100% of scored CVEs · Oct 14, 2026
Affects
Apache Software Foundation
Apache ActiveMQ and 15 more
CVSS base
9.8
Critical · 3 source(s)

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
Yes
can an attacker script the kill-chain steps
Technical impact
Total
partial · total control of the vulnerable component

Remediation

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

  • Documented patch — www.oracle.com (NIST National Vulnerability Database)
  • Documented mitigation — x-stream.github.io (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 (Apache Software Foundation Apache ActiveMQ, Apache Software Foundation Jmeter, Debian Debian Linux…).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. Apply the fixed version or the patch documented under Remediation.
  4. EPSS ahead of 100% of scored CVEs: prioritize it in the patch queue.
  5. Search available logs for exploit probes matching the vulnerability class (file handling), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Apache Software Foundation Apache ActiveMQ version 5.16.1< 5.15.14version 5.16.0 Vulnerable NIST National Vulnerability Database
Apache Software Foundation Jmeter < 5.5 Vulnerable NIST National Vulnerability Database
Debian Debian Linux version 9.0version 10.0version 11.0 Vulnerable NIST National Vulnerability Database
Fedoraproject Fedora version 34version 35version 33 Vulnerable NIST National Vulnerability Database
Netapp Oncommand Insight versions not specified by the source Vulnerable NIST National Vulnerability Database
Oracle Banking Enterprise Default Management version 2.12.0version 2.10.0 Vulnerable NIST National Vulnerability Database
Oracle Banking Platform version 2.4.0version 2.7.1version 2.12.0version 2.9.0 Vulnerable NIST National Vulnerability Database
Oracle Banking Virtual Account Management version 14.5.0version 14.3.0version 14.2.0 Vulnerable NIST National Vulnerability Database
Oracle Bi Publisher version 12.2.1.3.0version 5.5.0.0.0version 12.2.1.4.0 Vulnerable NIST National Vulnerability Database
Oracle Business Activity Monitoring version 12.2.1.3.0version 11.1.1.9.0version 12.2.1.4.0 Vulnerable NIST National Vulnerability Database
Oracle Communications Billing And Revenue Management Elastic Charging Engine version 12.0.0.3.0 Vulnerable NIST National Vulnerability Database
Oracle Communications Policy Management version 12.5.0 Vulnerable NIST National Vulnerability Database
Oracle Communications Unified Inventory Management version 7.4.1version 7.4.0version 7.3.5version 7.3.4version 7.3.2 Vulnerable NIST National Vulnerability Database
Oracle Retail Xstore Point Of Service version 17.0.4version 19.0.2version 18.0.3version 16.0.6 Vulnerable NIST National Vulnerability Database
Oracle WebCenter Portal version 12.2.1.4.0version 12.2.1.3.0version 11.1.1.9.0 Vulnerable NIST National Vulnerability Database
Xstream Xstream < 1.4.16 Vulnerable NIST National Vulnerability Database
Xstream Xstream version < 1.4.16 Vulnerable CVE Program (cve.org) e CISA ADP

Attack characteristics

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

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

Every base score collected

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

ScoreVersionSeverityExpl.ImpactScored by
9.8 CVSS 3.1 Critical 3.9 5.9 nvd@nist.gov via NIST National Vulnerability Database
6.1 CVSS 3.1 Medium 1.6 4.0 security-advisories@github.com via NIST National Vulnerability Database
6.1 CVSS 3.1 Medium — — GitHub_M via CVE Program (cve.org) e CISA ADP
7.5 CVSS 2.0 High 10.0 6.4 nvd@nist.gov via NIST National Vulnerability Database
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H (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 9.8 (NVD (NIST)) as a conservative provisional reference — not a definitive official score.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-434 · Unrestricted Upload of File with Dangerous Type

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 76.37%

Detection

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

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
  • Monitor file creation in web directories and paths with traversal sequences (../).
web/proxy/WAF logsnetwork IDS/IPSfile integrity (FIM)endpoint telemetry (EDR)

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · x-stream/xstream
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • 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 · 9.8
    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
  • 2021
  • CVE published
    Mar 22, 2021 · GitHub_M

Source activity

Repeated readings are counted rather than listed.

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

References

15 on the record

Elsewhere on this site

Apache Software Foundation
every CVE for this vendor
File handling
same class
CWE-434
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-83052 Improper Access Control in Oracle WebCenter Portal Sep 15, 2026
  • CVE-2026-83046 Improper Access Control in Oracle WebCenter Portal Sep 15, 2026
  • CVE-2026-83047 Improper Access Control in Oracle WebCenter Portal Sep 15, 2026
  • CVE-2026-83048 Improper Access Control in Oracle WebCenter Portal Sep 15, 2026
  • CVE-2026-83050 Improper Access Control in Oracle WebCenter Portal Sep 15, 2026
  • CVE-2026-83049 Improper Access Control in Oracle WebCenter Portal Sep 15, 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-2021-21346 is "XStream is vulnerable to an Arbitrary Code Execution attack", rated Critical. It affects Apache ActiveMQ (Apache Software Foundation); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 9.8 describes technical severity. EPSS 76.37% 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.

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