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NVD / CVE Program· CNA apache

CVE-2021-27850: Bypass of the fix for CVE-2019-0195

CriticalCVSS 9.8 · v3.1—Weaponized Fix available

Noroxi assessment

Priority: This week (action score 67/100)

  • A ready-made attack module is public (Metasploit, Nuclei); exploiting it takes no special expertise.
  • Public proof-of-concept code exists (GitHub); there is no record of exploitation in the wild.
  • Probability of exploitation in the next 30 days: 93.5% (FIRST EPSS); higher than 99.8% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: org.apache.tapestry:tapestry-core (Maven) 5.6.3, 5.7.1.

Don’t wait for the next maintenance window. Upgrade to org.apache.tapestry:tapestry-core (Maven) 5.6.3, 5.7.1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

Published
Apr 15, 2021
Updated
Jun 16, 2026
EPSS
93.5% · 99th percentile

Report tools

JSON

Action score

67

This week

Don’t wait for the next maintenance window.

CVSS
39 / 40 · 9.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
28 / 30 · 93.5%

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  • Not in KEV: no record of exploitation in the wild
  • Weaponized exploit exists
  • A fix has been released

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  • when exploit code appears or is weaponized
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  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
apachetapestry

Versions reported by the vendor

Affected version ranges reported by the assigning authority (apache). Independent of NVD's CPE analysis and usually ahead of it.

  • Apache Software Foundation Apache Tapestry

    • Apache Tapestry 5.5.0, Apache Tapestry 5.7.0affected
    • Apache Tapestry 5.4.5 and later · before Apache Tapestry 5.4.0*affected
    • Apache Tapestry 5.6.2 and later · before Apache Tapestry 5.6.0*affected

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • apache tapestry5.4.0 and later · before 5.6.2
  • apache tapestry5.7.0 and later · before 5.7.1

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Mavenorg.apache.tapestry:tapestry-corefrom 5.4.0 · before 5.6.35.6.3
Mavenorg.apache.tapestry:tapestry-corefrom 5.7.0 · before 5.7.15.7.1

Same product

apache: all records

Other highest-scoring records for the same primary product.

  • CVE-2019-0195Manipulating classpath asset file URLs, an attacker could guess the path to a known file in the classpath and have it downloaded.
    43Plan
  • CVE-2020-17531Deserialization flaw in EOL Tapestry 4.
    42Plan
  • CVE-2019-10071The code which checks HMAC in form submissions used String.equals() for comparisons, which results in a timing side channel for the…
    42Plan

Published before and after this one in the same product

  • ← EarlierCVE-2019-0207Sep 16, 2019 · Tapestry processes assets `/assets/ctx` using classes chain `StaticFilesFilter -> AssetDispatcher -> ContextResource`, which doesn't filter…
    31Monitor
  • ← EarlierCVE-2020-13953Sep 30, 2020 · In Apache Tapestry from 5.4.0 to 5.5.0, crafting specific URLs, an attacker can download files inside the WEB-INF folder of the WAR being…
    22Monitor
  • Later →CVE-2021-30638Apr 27, 2021 · An Information Disclosure due to insufficient input validation exists in Apache Tapestry 5.4.0 and later
    32Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Maven:org.apache.tapestry:tapestry-core5.6.3Package registry (OSV)
Maven:org.apache.tapestry:tapestry-core5.7.1Package registry (OSV)

Exploit status

Weaponized

A ready exploit tool or active in-the-wild use is known for this vulnerability. This should be your top priority.

Evidence

  • Metasploit module ×1
  • Nuclei detection template ×1
  • Proof-of-concept repository on GitHub ×4

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
SourceKindDate
Proof-of-concept repository on GitHub4 repositories2021-06-25 → 2022-07-07
Metasploit moduleauxiliary/gather/cve_2021_27850_apache_tapestry_hmac_keyApache Tapestry HMAC secret key leakauxiliary2021-04-15
Nuclei detection templateNuclei template CVE-2021-27850 —

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Metasploitsame day
  2. Published
  3. First PoC+71 d
  4. TodayNov 14, 2026+2039 d

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Not on record for this CVE: EPSS history · patch commit or PR link · variant or chain candidate · public bounty program.

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-200 · Exposure of Sensitive Information to an Unauthorized Actor

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

nvd-primary

Root cause

The extension requests broader permissions than its function needs and sends the data it collects out for purposes beyond its stated function.

The bug in code

The whole CWE-200 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

json
{  "permissions": ["tabs", "<all_urls>"],  "background": { "service_worker": "analytics.js" }}

Fixed

json
{  "permissions": ["activeTab"],  "host_permissions": ["https://yildiz.example/*"]}

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

References

Show all references (1 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records