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CVE-2021-21392

MEDIUM
Published 2021-04-12T21:50:14
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Expert Analysis

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CVSS Score

V3.1
6.3
/10
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:H/A:N
Base Score Metrics
Exploitability: N/A Impact: N/A

EPSS Score

v2025.03.14
0.002
probability
of exploitation in the wild

There is a 0.2% chance that this vulnerability will be exploited in the wild within the next 30 days.

Updated: 2025-06-25
Exploit Probability
Percentile: 0.425
Higher than 42.5% of all CVEs

Attack Vector Metrics

Attack Vector
NETWORK
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
REQUIRED
Scope
UNCHANGED

Impact Metrics

Confidentiality
LOW
Integrity
HIGH
Availability
NONE

Description

Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.28.0 requests to user provided domains were not restricted to external IP addresses when transitional IPv6 addresses were used. Outbound requests to federation, identity servers, when calculating the key validity for third-party invite events, sending push notifications, and generating URL previews are affected. This could cause Synapse to make requests to internal infrastructure on dual-stack networks. See referenced GitHub security advisory for details and workarounds.

Available Exploits

No exploits available for this CVE.

Related News

No news articles found for this CVE.

Affected Products

matrix-org

synapse

Affected Versions:

< 1.28.0

GitHub Security Advisories

Community-driven vulnerability intelligence from GitHub

✓ GitHub Reviewed HIGH

Open redirect via transitional IPv6 addresses on dual-stack networks

GHSA-5wrh-4jwv-5w78

Advisory Details

### Impact Requests to user provided domains were not restricted to external IP addresses when transitional IPv6 addresses were used. Outbound requests to federation, identity servers, when calculating the key validity for third-party invite events, sending push notifications, and generating URL previews are affected. This could cause Synapse to make requests to internal infrastructure on dual-stack networks. ### Patches This issue is fixed by #9240. ### Workarounds Outbound requests to the following address ranges can be blocked by a firewall, if unused for internal communication between systems: * `::ffff/80` * `::0000/80` (note that this IP range is considered deprecated by the IETF) * `2002::/16` (note that this IP range is considered deprecated by the IETF) ### References * [RFC3056](https://tools.ietf.org/html/rfc3056) * [RFC4291](https://tools.ietf.org/html/rfc4291)

Affected Packages

PyPI matrix-synapse
ECOSYSTEM: ≥0 <1.28.0rc1

CVSS Scoring

CVSS Score

7.5

CVSS Vector

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

References

WEB https://github.com/matrix-org/synapse/security/advisories/GHSA-5wrh-4jwv-5w78
ADVISORY https://nvd.nist.gov/vuln/detail/CVE-2021-21392
WEB https://github.com/matrix-org/synapse/pull/9240
WEB https://github.com/matrix-org/synapse/commit/4ca054a4eaa714d0befb4fc30b19a1131e52c9cc
PACKAGE https://github.com/matrix-org/synapse
WEB https://github.com/pypa/advisory-database/tree/main/vulns/matrix-synapse/PYSEC-2021-25.yaml
WEB https://lists.fedoraproject.org/archives/list/[email protected]/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY
WEB https://pypi.org/project/matrix-synapse

Advisory provided by GitHub Security Advisory Database. Published: April 13, 2021, Modified: September 30, 2024

References

https://pypi.org/project/matrix-synapse/
https://github.com/matrix-org/synapse/security/advisories/GHSA-5wrh-4jwv-5w78
https://github.com/matrix-org/synapse/pull/9240
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/
Published: 2021-04-12T21:50:14
Last Modified: 2024-08-03T18:09:15.930Z
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