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Open redirect via transitional IPv6 addresses on dual-stack networks

Moderate severity GitHub Reviewed Published Apr 12, 2021 in matrix-org/synapse • Updated Feb 1, 2023

Package

pip matrix-synapse (pip)

Affected versions

< 1.28.0

Patched versions

1.28.0

Description

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

References

@richvdh richvdh published to matrix-org/synapse Apr 12, 2021
Reviewed Apr 12, 2021
Published by the National Vulnerability Database Apr 12, 2021
Published to the GitHub Advisory Database Apr 13, 2021
Last updated Feb 1, 2023

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
Low
User interaction
Required
Scope
Unchanged
Confidentiality
Low
Integrity
High
Availability
None

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:H/A:N

EPSS score

0.086%
(37th percentile)

Weaknesses

CVE ID

CVE-2021-21392

GHSA ID

GHSA-5wrh-4jwv-5w78

Source code

Credits

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