CVE-2021-27905Public exploitNetwork attack vector

Server-side request forgery via unchecked replication URL

Published Apr 13, 2021 · Updated Aug 3, 2024

SSRF in Apache Solr 7.0.0 through 7.7.3 and 8.0.0 through 8.8.1 allows remote attackers to make server-side requests. The ReplicationHandler accepts masterUrl or leaderUrl as a replication source without checking it against the shard URL allowlist. Exposure requires access to /replication, which Apache states should normally be internal; successful requests originate from the Solr host.

CVSS severity9.8
Critical
EPSS probability93.05%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

SSRF in Apache Solr 7.0.0 through 7.7.3 and 8.0.0 through 8.8.1 allows remote attackers to make server-side requests. The ReplicationHandler accepts masterUrl or leaderUrl as a replication source without checking it against the shard URL allowlist. Exposure requires access to /replication, which Apache states should normally be internal; successful requests originate from the Solr host.

The record

CVE
CVE-2021-27905
Published
Apr 13, 2021
Updated
Aug 3, 2024
Vendor
The Apache Software Foundation
Product
Apache Solr
Classifications
CWE-918, T1090
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 13, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=Apache Solr <8.8.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache Solrversion=Apache Solr <8.8.2

Published CVSS scores

9.8UbuntuCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-918Server-Side Request Forgery (SSRF)
T1090Proxy

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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