Security readout for executives and security teams
Plain-English summary
CVE-2021-39150 affects XStream, a Java XML serialization library. Vulnerable applications processing attacker-controlled XStream input could be induced to request internal, non-public resources. This creates SSRF risk and may expose sensitive internal services. The vendor says users using a strict type whitelist are not affected.
Executive priority
Treat as high priority where XStream processes untrusted input, especially in internet-facing or partner-facing systems. Prioritize upgrade and configuration validation, but avoid declaring emergency active-exploitation response without additional evidence.
Technical view
Affected XStream versions before 1.4.18 can trigger SSRF during PriorityQueue unmarshalling on Java runtimes 8 through 14, when unsafe input is processed. The issue is tied to deserialization behavior and XStream security framework configuration, especially reliance on the default blacklist rather than a minimal type whitelist.
Likely exposure
Exposure is most likely in Java applications or products embedding XStream before 1.4.18 and accepting XML streams from low-privileged or remote users. Risk is lower where XStream’s security framework uses a minimal required type whitelist.
Exploitation context
The source bundle does not show CISA KEV listing or cited evidence of active exploitation. CVSS indicates network attack vector, high complexity, low privileges, no user interaction, and high confidentiality, integrity, and availability impact.
Researcher notes
Key conditions are vulnerable XStream version, Java 8-14 runtime context, attacker-controlled processed input stream, and insufficient type allowlisting. Evidence provided supports SSRF via PriorityQueue unmarshalling, but does not include exploit prevalence, public exploitation confirmation, or complete downstream product impact.
Mitigation direction
- Upgrade XStream to version 1.4.18 or later.
- Configure XStream security with a minimal required type whitelist.
- Do not rely on the default blacklist for affected versions.
- Apply relevant Debian, Fedora, Oracle, or NetApp vendor updates where XStream is bundled.
- Check vendor guidance for product-specific remediation details.
Validation and detection
- Inventory applications and products that include x-stream:xstream or libxstream-java.
- Confirm all detected XStream versions are 1.4.18 or later.
- Review XStream security configuration for explicit minimal type whitelisting.
- Identify endpoints or jobs that process externally supplied XStream XML.
- Check vendor advisories for bundled XStream exposure in third-party products.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-502: Code execution behavior lookup
Code execution and unsafe deserialization weaknesses often justify reviewing execution behavior and process telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCWE-918: Information exposure and cloud metadata lookup
Information exposure and SSRF weaknesses can make discovery, cloud metadata, and credential material review relevant. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupCVE-2021-39150 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 8.5 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H1.86Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
8.5HighVector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:H/A:H
Source materials
- CVE List V5 sourceCVE List V5
- https://github.com/x-stream/xstream/security/advisories/GHSA-cxfm-5m4g-x7xpCVE reference · x_refsource_CONFIRM
- https://x-stream.github.io/CVE-2021-39150.htmlCVE reference · x_refsource_MISC
- [debian-lts-announce] 20210929 [SECURITY] [DLA 2769-1] libxstream-java security updateCVE reference · mailing-list, x_refsource_MLIST
- FEDORA-2021-fbad11014aCVE reference · vendor-advisory, x_refsource_FEDORA
- FEDORA-2021-d894ca87dcCVE reference · vendor-advisory, x_refsource_FEDORA
- FEDORA-2021-5e376c0ed9CVE reference · vendor-advisory, x_refsource_FEDORA
- DSA-5004CVE reference · vendor-advisory, x_refsource_DEBIAN
- https://www.oracle.com/security-alerts/cpujan2022.htmlCVE reference · x_refsource_MISC
- https://security.netapp.com/advisory/ntap-20210923-0003/CVE reference · x_refsource_CONFIRM
- https://www.oracle.com/security-alerts/cpuapr2022.htmlCVE reference · x_refsource_MISC
- https://www.oracle.com/security-alerts/cpujul2022.htmlCVE reference · x_refsource_MISC
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Deserialization of Untrusted Data
Deserialization of Untrusted Data represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.
Server-Side Request Forgery (SSRF)
Server-Side Request Forgery (SSRF) represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.