GHSL-2026-105: Removed Signal group members can modify previously sent messages on a recipient’s iOS device
Published Sep 21, 2026
·Updated
Removed Signal group members can bypass thread-scoping checks to modify messages they previously sent, but only in a targeted recipient's local view of the group.
Affected Software
1 affected component
Signal Signal iOS
Event History
Sep 21, 2026
Advisory Published
via GitHub Security Lab·12:00 AM
Data Sourced
via GitHub Security Lab·12:00 AM
Description
Frequently Asked Questions
1
Who can exploit this issue?
A person who was previously a member of a Signal group and has sent messages in that group can exploit it after being removed, by targeting a recipient's local view of the group.
2
What is the impact on affected recipients?
The attacker can modify messages they previously sent, but the modification is limited to the local group view of a targeted recipient rather than the group for all participants.