CVE-2021-27850

CRITICALNVD 9.89.8—
EchelonGraph scoreHIGH confidence

Score elevated to 9.8 because EPSS predicts 94% probability of exploitation within the next 30 days (top 0.1% of all CVEs). NVD baseline CVSS 9.8 retained for reference. Confidence: see factors.

Triggered by: EPSS exploit prediction ≥85%
Sources: epss, nvd
Weaponized
9.8
EchelonGraph verdictPatch this weekExploitation is likely or a public exploit exists.
  • High exploitation likelihood — EPSS 94%
CISA-KEV: Not listedEPSS: 94%CVSS: 9.8Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

A critical unauthenticated remote code execution vulnerability was found all recent versions of Apache Tapestry. The affected versions include 5.4.5, 5.5.0, 5.6.2 and 5.7.0. The vulnerability I have found is a bypass of the fix for CVE-2019-0195. Recap: Before the fix of CVE-2019-0195 it was possible to download arbitrary class files from the classpath by providing a crafted asset file URL. An attacker was able to download the file AppModule.class by requesting the URL http://localhost:8080/assets/something/services/AppModule.class which contains a HMAC secret key. The fix for that bug was a blacklist filter that checks if the URL ends with .class, .properties or .xml. Bypass: Unfortunately, the blacklist solution can simply be bypassed by appending a / at the end of the URL: http://localhost:8080/assets/something/services/AppModule.class/ The slash is stripped after the blacklist check and the file AppModule.class is loaded into the response. This class usually contains the HMAC secret key which is used to sign serialized Java objects. With the knowledge of that key an attacker can sign a Java gadget chain that leads to RCE (e.g. CommonsBeanUtils1 from ysoserial). Solution for this vulnerability: * For Apache Tapestry 5.4.0 to 5.6.1, upgrade to 5.6.2 or later. * For Apache Tapestry 5.7.0, upgrade to 5.7.1 or later.

CVSS v3
9.8
EG Score
9.8(high)
EPSS
99.8%
KEV
Not listed

Published

April 15, 2021

Last Modified

November 21, 2024

Advisory Details (3)

Auto-updated Jun 13, 2026
No patch confirmed yet.
generic

NetApp Product Security

https://security.netapp.com/advisory/ntap-20210528-0002/
generic
https://lists.apache.org/thread.html/r237ff7f286bda31682c254550c1ebf92b0ec61329b32fbeb2d1c8751%40%3Cusers.tapestry.apache.org%3E
generic

oss-security - CVE-2021-27850: Apache Tapestry: Bypass of the fix for CVE-2019-0195

http://www.openwall.com/lists/oss-security/2021/04/15/1

Affected Packages

(1 across 1 ecosystem)
Maven(1)
PackageVulnerable rangeFixed inDependents
org.apache.tapestry:tapestry-core5.7.05.7.1—

Weakness Classification(2)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 5× in last 7d / 11× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

  1. 2026-07-22 14:06 UTCEPSS rescore
  2. 2026-07-22 14:06 UTCEPSS rescore
  3. 2026-07-21 15:22 UTCEPSS rescore
  4. 2026-07-21 15:22 UTCEPSS rescore
  5. 2026-07-18 21:59 UTCOSV refresh
  6. 2026-07-15 16:55 UTCEPSS rescore
  7. 2026-07-15 16:55 UTCEPSS rescore
  8. 2026-07-01 15:03 UTCEPSS rescore
  9. 2026-07-01 05:18 UTCOSV refresh
  10. 2026-06-23 21:31 UTCEPSS rescore
  11. 2026-06-23 21:31 UTCEPSS rescore
  12. 2026-06-22 14:24 UTCEPSS rescore
  13. 2026-06-22 14:24 UTCEPSS rescore
  14. 2026-06-18 17:51 UTCEPSS rescore
  15. 2026-06-18 17:51 UTCEPSS rescore
  16. 2026-06-15 17:46 UTCEPSS rescore
  17. 2026-06-13 08:43 UTCOSV refresh
  18. 2026-06-08 14:15 UTCEPSS rescore
  19. 2026-05-28 13:43 UTCEPSS rescore
  20. 2026-05-28 13:43 UTCEPSS rescore
  21. 2026-05-26 18:14 UTCEG score recompute

Publicly available exploits

(5 references)

Working exploit code is in the public domain (1 Metasploit module) (3 GitHub PoCs). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • GitHub PoCOvi3/CVE_2021_27850_POC
    First seen Jul 2, 2021

    Apache Tapestry CVE-2021-27850 PoC

    Open source ↗
  • GitHub PoCdorkerdevil/CVE-2021-27850_POC
    First seen Jun 26, 2021

    A Proof of concept for CVE-2021-27850 affecting Apache Tapestry and leading to unauthencticated remote code execution.

    Open source ↗
  • GitHub PoCkahla-sec/CVE-2021-27850_POC
    First seen Jun 25, 2021

    A Proof of concept for CVE-2021-27850 affecting Apache Tapestry and leading to unauthencticated remote code execution.

    Open source ↗
  • Metasploitauxiliary/gather/cve_2021_27850_apache_tapestry_hmac_key✓ verified
    First seen Apr 15, 2021

    Apache Tapestry HMAC secret key leak

    Open source ↗
  • Nucleihttp/cves/2021/CVE-2021-27850.yaml
    First seen Jan 1, 2021

    Apache Tapestry - Remote Code Execution

    Open source ↗

Related CVEs(same CWE)

Frequently asked(5)

What is CVE-2021-27850?
CVE-2021-27850 is a critical vulnerability published on April 15, 2021. A critical unauthenticated remote code execution vulnerability was found all recent versions of Apache Tapestry. The affected versions include 5.4.5, 5.5.0, 5.6.2 and 5.7.0. The vulnerability I have found is a bypass of the fix for CVE-2019-0195. Recap: Before the fix of CVE-2019-0195 it was…
When was CVE-2021-27850 disclosed?
CVE-2021-27850 was first published in the National Vulnerability Database on April 15, 2021, with the most recent update on November 21, 2024. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2021-27850 actively exploited?
CVE-2021-27850 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 99.8% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2021-27850?
CVE-2021-27850 has a CVSS v3 base score of 9.8 (NVD).
How do I remediate CVE-2021-27850?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2021-27850, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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