Backslash in label value is not properly url-decoded #4804
Description
What did you do?
When creating a silence that contains a label value ending with a Windows path (e.g., E:), the Alertmanager UI incorrectly handles the backslash.
Example filter:
{volume_mount_point="E:\"}
After url decoding, Alertmanager treats the trailing backslash as an invalid escape sequence and fails to parse the label selector.
What did you expect to see?
Alertmanager UI should properly escape backslashes when constructing or decoding silence URLs.
Example:
volume_mount_point="E:\\" should be encoded in URL as E:%5C%5C and decoded back into a valid label selector instead of causing an parsing error.
What did you see instead? Under which circumstances?
The UI decodes E:%5C into E:\ but the backslash is not properly escaped, resulting in: volume_mount_point="E:\"
This causes the silence creation page to fail to load the selector.
Link:
https://infra-prom-alert.ipt.inventec.net/#/silences/new?filter=%7Balertname%3D%22MSSQLNotHealthDisks%22%2C%20instance%3D%22mssql-exporter%3A9273%22%2C%20job%3D%22mssql%22%2C%20measurement_db_type%3D%22SQLServer%22%2C%20server_name%3D%22IPT-F3FISDB%22%2C%20severity%3D%22red%22%2C%20sql_instance%3D%22IPT-F3FISDB%22%2C%20volume_mount_point%3D%22E%3A%5C%22%7D
System information
No response
Alertmanager version
alertmanager, version 0.28.1 (branch: HEAD, revision: b2099eaa2c9ebc25edb26517cb9c732738e93910)
build user: root@fa3ca569dfe4
build date: 20250307-15:05:18
go version: go1.23.7
platform: linux/amd64
tags: netgo
Alertmanager configuration file
Prometheus version
Prometheus configuration file
Logs