CVE Intelligence
High SSRF exploit reference

CVE-2020-26258 — Server-Side Forgery Request can be activated unmarshalling with XStream

XStream is a Java library to serialize objects to XML and back again. In XStream before version 1.4.15, a Server-Side Forgery Request vulnerability can be activated when unmarshalling. The vulnerability may allow a remote attacker to request data from internal resources that are not publicly available only by manipulating the processed input stream. If you rely on XStream's default blacklist of the Security Framework, you will have to use at least version 1.4.15. The reported vulnerability does not exist if running Java 15 or higher. No user is affected who followed the recommendation to setup XStream's Security Framework with a whitelist! Anyone relying on XStream's default blacklist can immediately switch to a whilelist for the allowed types to avoid the vulnerability. Users of XStream 1.4.14 or below who still want to use XStream default blacklist can use a workaround described in more detailed in the referenced advisories.

Published Dec 15, 2020 · 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.

Detection templates (Nuclei) · 1
How the score was calculated
  • Public exploit/PoC (nuclei)+4
  • EPSS 81.8% (30-day exploitation probability)+15
  • Technical severity (high)+6
  • 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
81.82%
ahead of 100% of scored CVEs · Oct 14, 2026
Affects
Apache Software Foundation
Struts and 3 more
CVSS base
7.7
High · 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
Partial
partial · total control of the vulnerable component

Remediation

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

  • Documented mitigation — github.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 Struts, Debian Debian Linux, Fedoraproject Fedora…).
  2. Apply the documented mitigations until a definitive fix is available.
  3. EPSS ahead of 100% of scored CVEs: prioritize it in the patch queue.
  4. Search available logs for exploit probes matching the vulnerability class (ssrf), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Apache Software Foundation Struts < 6.0.0 Vulnerable NIST National Vulnerability Database
Debian Debian Linux version 9.0version 10.0 Vulnerable NIST National Vulnerability Database
Fedoraproject Fedora version 33version 34version 35 Vulnerable NIST National Vulnerability Database
Xstream Xstream < 1.4.15 Vulnerable NIST National Vulnerability Database
Xstream Xstream version < 1.4.15 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
Low
User interaction
None
Scope
Changed
Confidentiality
High
Integrity
None
Availability
None

Every base score collected

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

ScoreVersionSeverityExpl.ImpactScored by
7.7 CVSS 3.1 High 3.1 4.0 nvd@nist.gov via NIST National Vulnerability Database
6.3 CVSS 3.1 Medium 1.8 4.0 security-advisories@github.com via NIST National Vulnerability Database
6.3 CVSS 3.1 Medium — — GitHub_M via CVE Program (cve.org) e CISA ADP
5.0 CVSS 2.0 Medium 10.0 2.9 nvd@nist.gov via NIST National Vulnerability Database
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N (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 7.7 (NVD (NIST)) as a conservative provisional reference — not a definitive official score.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-918 · Server-Side Request Forgery (SSRF)

Other CVEs with this weakness →

Public exploits, PoCs and detection templates

Public code that demonstrates or tests the flaw raises the odds of mass exploitation — and Nuclei templates help find vulnerable assets in your environment.

Detection templates (Nuclei)

Warning: public PoCs are sometimes disguised malware. Use them only for authorized testing in an isolated environment. This portal does not host exploit code — it only points to the sources.

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 81.82%

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 outbound requests from the server to internal IPs and cloud metadata endpoints.
web/proxy/WAF logsnetwork IDS/IPSegress traffic

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 · 7.7
    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
  • 2020
  • CVE published
    Dec 15, 2020 · GitHub_M

Source activity

Repeated readings are counted rather than listed.

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

References

14 on the record

Elsewhere on this site

Apache Software Foundation
every CVE for this vendor
SSRF
same class
CWE-918
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-104711 Apache Struts: OGNL injection in the legacy RESTful action mapper 10d
  • CVE-2026-104714 Apache Struts: Shared message formatter exposes date and time values across concurrent requests 10d
  • CVE-2026-104713 Apache Struts: Unbounded request body read in the REST plugin 10d
  • CVE-2026-104712 Apache Struts: Disproportionate response size when rendering BigDecimal request parameters 10d
  • CVE-2026-73631 Apache Struts: Shared parsing state in the JSON plugin Aug 15, 2026
  • CVE-2026-73632 Apache Struts: Shared serialization state in the JSON plugin Aug 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-2020-26258 is "Server-Side Forgery Request can be activated unmarshalling with XStream", rated High. It affects Struts (Apache Software Foundation); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 7.7 describes technical severity. EPSS 81.82% 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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