CVE-2021-27905

CVE-2021-27905 is a critical-severity vulnerability in Apache Solr with a CVSS 3.x base score of 9.8. Its EPSS exploit-prediction score of 93% places it in the 100th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-918.

Key facts

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.

Frequently asked questions

What is CVE-2021-27905?
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.
How severe is CVE-2021-27905?
CVE-2021-27905 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2021-27905 being actively exploited?
It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 93% (100th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-27905?
CVE-2021-27905 affects Apache Solr. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-27905?
Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-27905 published?
CVE-2021-27905 was published on 2021-04-13 and last updated on 2026-06-17.

References

Affected products (1)

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