`CVE-2021-27905` Apache Solr

Affected software	Apache Solr
Severity	9.8 Critical CVSS 3.1 2 scores
Fixed in	`8.8.2`
Weakness	Server-side request forgery (CWE-918)
Published	13 Apr 2021
Updated	13 Nov 2026

Description

The ReplicationHandler (normally registered at "/replication" under a Solr core) in Apache Solr has a "masterUrl" (also "leaderUrl" alias) parameter that is used to designate another ReplicationHandler on another Solr core to replicate index data into the local core. To prevent a SSRF vulnerability, Solr ought to check these parameters against a similar configuration it uses for the "shards" parameter. Prior to this bug getting fixed, it did not. This problem affects essentially all Solr versions prior to it getting fixed in 8.8.2.

Exploitation status

Working exploit published

A reviewed exploit catalogue lists ready-to-run exploit code for this CVE.

CISA KEV not listed
VulnCheck KEV not listed
CISA Vulnrichment no assessment published
Indexed PoC 6 indexed Published artifacts you can open, in GitHub PoC, Nuclei; first seen 2021-04-21.
EPSS 93% chance in 30 days A model's forecast, not a report of exploitation. Higher than 99.8% of all scored CVEs.

3 of these are GitHub repositories with fewer than 5 stars. They are listed for reference and don't count toward the exploitation status above.

Index	Artifact	Stars	First seen
GitHub PoC	Apache Solr SSRF(CVE-2021-27905)	70	2021-04-21
GitHub PoC	[CVE-2021-27905] Apache Solr ReplicationHandler Server Side Request Forgery (SSRF)	6	2021-08-10
GitHub PoC	POC for LFI related to CVE-2021-27905	3	2022-11-03
GitHub PoC	Apache Solr < 8.8.2 Server Side Request Forgery	2	2025-10-18
GitHub PoC	CVE-2021-27905		2021-04-25
Nuclei	Apache Solr <=8.8.1 - Server-Side Request Forgery

Waratek protection

Rule in development

Waratek is working on a rule for this CVE. No rule is available yet, and it isn't certain the rule will work.

Current target: Q2 2027 (may change)

Protection none
Action in development patch rule; current target Q2 2027, may change
Review human Researcher
Record active

Decided by	A researcher's recorded decision for this specific CVE
Finding	A researcher set this CVE's status to Rule in development, naming the ARMR SSRF rule (in development).

Decided by

A researcher's recorded decision for this specific CVE

Finding

A researcher set this CVE's status to Rule in development, naming the ARMR SSRF rule (in development).

Waratek research note

written 2026-11-13

Written by a Waratek engineer who reviewed this CVE. Their decision sets the status above, ahead of every automated rule except a withdrawal.

Comments

Rule Name: SSRF rule (in development)

SSRF in Solr's ReplicationHandler: the masterUrl (or leaderUrl) request parameter on /replication?command=fetchindex makes Solr connect to a server the attacker chooses. An SSRF rule in development is meant to block an outbound request to an address taken from request parameters. Nothing blocks this CVE until that rule ships.

CVSS

9.8 CRITICAL v3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H 2 metrics

We show the highest score from the newest CVSS version. Scores from different versions can't be compared, and the first score listed is sometimes a 0.0 placeholder.

Version Score Band Vector Assigner Type

CVSS 3.1 9.8 CRITICAL CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H NVD Primary published

CVSS 2.0 7.5 none AV:N/AC:L/Au:N/C:P/I:P/A:P NVD Primary

Version	Score	Band	Vector	Assigner	Type
CVSS 3.1	9.8	CRITICAL	`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`	NVD	Primary	published
CVSS 2.0	7.5	none	`AV:N/AC:L/Au:N/C:P/I:P/A:P`	NVD	Primary

Affected software and releases

Maven packages

Affected and fixed versions, from OSV.dev

Package Introduced Fixed Last affected

org.apache.solr:solr-parent 0 8.8.2 unbounded

Package	Introduced	Fixed	Last affected
`org.apache.solr:solr-parent`	0	`8.8.2`	unbounded

Products and versions

2 products, 2 version entries

Source	Vendor	Product	Scheme	Affected versions
nvd	apache	solr	generic	＜ 8.8.2
osv	org.apache.solr	solr-parent	generic	＜ 8.8.2

Source

Vendor

Product

Scheme

Affected versions

nvd

apache

solr

generic

＜ 8.8.2

osv

org.apache.solr

solr-parent

generic

＜ 8.8.2

References

URL	Tags
https://lists.apache.org/thread.html/r0ddc3a82bd7523b1453cb7a5e09eb5559517145425074a42eb326b10%40%3Cannounce.apache.org%3E	WEB
https://lists.apache.org/thread.html/r140128dc6bb4f4e0b6a39e962c7ca25a8cbc8e48ed766176c931fccc@%3Cusers.solr.apache.org%3E	WEB
https://lists.apache.org/thread.html/r3da74965aba2b5f5744b7289ad447306eeb2940c872801819faa9314@%3Cusers.solr.apache.org%3E	WEB
https://lists.apache.org/thread.html/r6ccec7fc54d82591b23c143f1f6a6e38f6e03e75db70870e4cb14a1a@%3Ccommits.ofbiz.apache.org%3E	WEB
https://lists.apache.org/thread.html/r720a4a0497fc90bad5feec8aa18b777912ee15c7eeb5f882adbf523e@%3Ccommits.ofbiz.apache.org%3E	WEB
https://lists.apache.org/thread.html/r78a3a4f1138a1608b0c6d4a2ee7647848c1a20b0d5c652cd9b02c25a@%3Ccommits.ofbiz.apache.org%3E	WEB
https://lists.apache.org/thread.html/r8f1152a43c36d878bbeb5a92f261e9efaf3af313b033d7acfccea59d@%3Cnotifications.ofbiz.apache.org%3E	WEB
https://lists.apache.org/thread.html/r95df34bb158375948da82b4dfe9a1b5d528572d586584162f8f5aeef@%3Cusers.solr.apache.org%3E	WEB
https://lists.apache.org/thread.html/rae9ccaecce9859f709ed1458545d90a4c07163070dc98b5e9e59057f@%3Cnotifications.ofbiz.apache.org%3E	WEB
https://lists.apache.org/thread.html/rd232d77c57a8ce172359ab098df9512d8b37373ab87c444be911b430@%3Cnotifications.ofbiz.apache.org%3E	WEB

URL

Timeline

Published	2021-04-13	By the CVE Program.
NVD record modified	2026-06-17	NVD's own last-modified date for this record.
Classification created	2026-11-13	First commit adding this CVE's research note.
Last VRT activity	2026-11-13	Most recent commit touching this CVE's classification, patch or rule file.

Published

2021-04-13

By the CVE Program.

NVD record modified

2026-06-17

NVD's own last-modified date for this record.

Classification created

2026-11-13

First commit adding this CVE's research note.

Last VRT activity

2026-11-13

Most recent commit touching this CVE's classification, patch or rule file.

How VRT decided (4 of 24 rules ran)

4 of 24 rules ran. The rest didn't run because an earlier rule had already settled the CVE.

# Rule Outcome Status Detail

identity: Does this identifier describe a vulnerability at all? the first rule that matches decides

1 rejected no match CVE Program withdrawal of this identifier

scope: Is it a vulnerability Waratek protects? the first rule that matches decides

2 armr-patch-file no match An ARMR patch file on disk for this CVE

3 armr-secure-rule-file no match An ARMR security-rule template on disk for this CVE

4 manual-classification decided it matched Rule in development A researcher set this CVE's status to Rule in development, naming the ARMR SSRF rule (in development).

5 manual classification not reached Manual classification of this CVE in the legacy dataset

6 non-java-upstream not reached A root cause in non-Java code: an OS kernel, a C library, or a bundled runtime

7 oracle-component not reached The defect being in a component of a tracked product the agent does not reach: JavaFX, the Java SE installer, the JInitiator browser plug-in, the native WebLogic proxy plug-in, or a native part of Oracle Application Server or Collaboration Suite (HTTP Server, Web Cache, Internet Directory, mail and calendar servers). Oracle gives these no CPE of their own and names them only in the description.

8 java-client-side not reached Oracle's own risk-matrix note saying the CVE is reached only through untrusted code in the Java sandbox (applets, Web Start) or only through a client installation of Java, so a server running its own trusted code is not exposed

9 osv-maven not reached An OSV.dev record of this CVE affecting a package published to Maven Central. When every such package is one business applications do not use (Minecraft mods and launchers, Fastjson) and no tracked product is named by CPE, it settles the CVE as Outside Waratek scope instead

10 cna-maven-package not reached An affected Maven artifact named by the CNA itself

11 known-cpe-product not reached An NVD CPE naming a product ARMR tracks

12 cna-cpe-product not reached A CPE the CNA published naming a tracked product. Oracle publishes these on advisory day, months before NVD.

13 oracle-advisory-family not reached A tracked product family named in Oracle's own risk matrix. CPE cannot carry a suite name, only a module.

14 cna-named-product not reached A tracked product named in words by the CVE's own CNA, on a record with no CPE yet. Apache and Eclipse publish these on advisory day, before NVD adds CPE data.

15 non-deployable-product not reached The only affected product being a sealed appliance image, where Java runs but no -javaagent can be attached

16 unmatched-product not reached No tracked product matched above, and none present at all

disposition: What do we do about one that is? every rule runs

17 patch-hint not reached A reference pointing at the upstream fix: a commit, a PR, a Red Hat bug

18 open-source-maven not reached The affected package being open source on Maven, so the fix can be read

19 poc-derivable not reached An indexed exploit clearing the evidence bar to reverse-engineer, where there is no source to read

20 no-exploit not reached Nothing to build a rule from yet: no published exploit, no CISA record of exploitation and no source-level change to read

21 secure-rule-match not reached A vulnerability class already blocked by an ARMR security rule

22 exploited-no-fix-or-poc not reached Somebody exploiting this CVE (a CISA or VulnCheck KEV listing, or a CISA verdict of active exploitation), with no fix, source code or PoC to build a rule from

23 below-action-threshold not reached Medium or Low severity, no CISA or VulnCheck KEV listing, no PoC clearing the evidence bar, no CISA verdict, no Oracle advisory

24 no-exploit-published not reached Exploit code for this candidate, published in a reviewed catalogue or a GitHub repository with 5 or more stars, or in use per CISA or VulnCheck; not only a CISA verdict, a forecast, or nothing at all

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