CVE-2021-26086
Affected versions of Atlassian Jira Server and Data Center allow remote attackers to read particular files via a path traversal vulnerability in the /WEB-INF/web.xml endpoint. The affected versions are before version 8.5.14, from version 8.6.0 before 8.13.6, and from version 8.14.0 before 8.16.1.
do firstApply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
Can a WAF block it? Yes. The attack uses a path traversal in an HTTP request to the /WEB-INF/web.xml endpoint, which includes ../ sequences that normal requests do not contain, allowing a WAF to detect and block such malicious input. A WAF rule can match ../ sequences in the /WEB-INF/web.xml endpoint. No tracked WAF vendor has published a rule for this CVE yet, so you would write it yourself.
What a custom rule would match: ../ sequences in the /WEB-INF/web.xml endpoint
Also consider: patch · custom WAF rule · canonical path validation
Based on an AI reading of the CVE description, and no vendor rule found yet. We check Cloudflare, AWS, Google Cloud Armor and Azure; for Akamai, Imperva, Fastly, F5, ask your vendor.
Is CVE-2021-26086 being exploited?
Yes. CVE-2021-26086 appears in CISA's Known Exploited Vulnerabilities catalog, which means exploitation in the wild has been confirmed and reported. Treat it as active rather than theoretical, and patch it ahead of higher-scoring vulnerabilities that carry no exploitation evidence.
How severe is CVE-2021-26086?
CVE-2021-26086 is rated Medium with a CVSS score of 5.3. Severity describes how bad exploitation would be, not how likely it is: pair it with exploitation evidence before deciding what to patch first.
Is there a patch for CVE-2021-26086?
Yes. A fix has been recorded for CVE-2021-26086. The vendor advisory is the authority on the exact fixed version — apply it from there rather than from a summary.
What does CVE-2021-26086 affect?
CVE-2021-26086 affects atlassian:jira_data_center, atlassian:jira_server. Confirm the exact affected versions against the vendor advisory before deciding you are exposed.
Exploitation status reflects CISA's KEV catalog as we last synced it. Check the catalog directly.
- affected< 8.5.14
- affected>= 8.6.0 and < unspecified
- affected< 8.13.6
- affected>= 8.14.0 and < unspecified
- affected< 8.16.1
- affected< 8.5.14
- affected>= 8.6.0 and < unspecified
- affected< 8.13.6
- affected>= 8.14.0 and < unspecified
- affected< 8.16.1
As published in the CVE Program record. A version outside these ranges is not a statement that it is unaffected — vendors sometimes understate a range, and distribution-backported builds carry upstream numbers that do not reflect what was patched into them.
public exploits
Public exploit code: 1 on Exploit-DB · 3 GitHub proofs of concept · 1 Nuclei template
- Atlassian Jira Server Data Center 8.16.0 - Arbitrary File Read · webapps · 6 Oct 2021
- Atlassian Jira Limited - Local File Inclusion · detection template · medium
Listed so you can judge urgency, not as a recommendation to run anything. GitHub “proofs of concept” are unvetted: some are fake or carry malware. Exploit-DB marks the entries its staff verified.
cisa ssvc
- exploitation
- active
- automatable
- yes
- technical impact
- partial
Assessed by CISA 13 Nov 2024 (SSVC 2.0.3).
timeline
- 16 Aug 2021Published
- 5 Sept 2021First public exploit or proof of concept · 20 days later
- 12 Nov 2024Added to CISA KEV (exploited in the wild) · 1,164 days (about 3 years) later
- 13 Nov 2024CISA SSVC assessment: exploitation active · 2 days later
- 3 Dec 2024CISA remediation due date (US federal agencies) · 19 days later
- 21 Oct 2025CVE record last updated · 323 days (about 11 months) later
- 2 Nov 2026Analysed by vulneraibility.com · 377 days (about 1 year) later
- Linkjira.atlassian.com /browse/JRASERVER-72695
- Linkpacketstormsecurity.com /files/164405/Atlassian-Jira-Server-Data-Center-8.4.0-File-Read.html
- Linkcisa.gov /known-exploited-vulnerabilities-catalog?field_cve=CVE-2021-26086
sources
- CVE List (CVE.org): description, affected versions, references; CVE Terms of Use
- NVD: CVSS and CPE data
- CISA KEV catalog: exploitation, date added, due date
- CISA Vulnrichment (ADP): SSVC decision points
- FIRST EPSS: exploit probability and percentile
- Exploit-DB: published exploits
- Nuclei templates: detection templates
- PoC-in-GitHub: GitHub repositories that claim a proof of concept
- Summary, impact and triage tags: written by our AI analysis pipeline from the sources above. Check them against the sources.