ufw delete can confuse protocol-specific rule with otherwise matching 'proto any' rule
Affects | Status | Importance | Assigned to | Milestone | |
---|---|---|---|---|---|
ufw |
Fix Released
|
High
|
Jamie Strandboge | ||
ufw (Ubuntu) |
Fix Released
|
Undecided
|
Jamie Strandboge | ||
Bionic |
Fix Released
|
Medium
|
Mauricio Faria de Oliveira | ||
Focal |
Fix Released
|
Medium
|
Mauricio Faria de Oliveira | ||
Hirsute |
Fix Released
|
Medium
|
Mauricio Faria de Oliveira |
Bug Description
[Impact]
* The deletion of a rule without the 'proto' field
that has a similar rule *with* the 'proto' field
might delete the wrong rule (the latter).
* This might cause services to be inaccessible or
incorrectly allowed, depending on rule ordering
(read original description below for examples.)
[Test Steps]
* Add rules:
ufw allow from 1.1.1.1 port 1111 proto tcp
ufw allow from 2.2.2.2 port 2222 proto tcp
ufw allow from 1.1.1.1 port 1111
* Check iptables:
iptables -L ufw-user-input -n
...
ACCEPT tcp -- 1.1.1.1 0.0.0.0/0 tcp spt:1111
ACCEPT tcp -- 2.2.2.2 0.0.0.0/0 tcp spt:2222
ACCEPT tcp -- 1.1.1.1 0.0.0.0/0 tcp spt:1111
ACCEPT udp -- 1.1.1.1 0.0.0.0/0 udp spt:1111
* Delete the third rule above
ufw status numbered
yes | ufw delete 3
* Check iptables again:
iptables -L ufw-user-input -n
Observed: (deleted tcp line from first rule, and udp line from third rule)
...
ACCEPT tcp -- 2.2.2.2 0.0.0.0/0 tcp spt:2222
ACCEPT tcp -- 1.1.1.1 0.0.0.0/0 tcp spt:1111
Expected: (deleted both tcp and udp lines from third rule)
...
ACCEPT tcp -- 1.1.1.1 0.0.0.0/0 tcp spt:1111
ACCEPT tcp -- 2.2.2.2 0.0.0.0/0 tcp spt:2222
[Regression Potential]
* Potential regressions would be observed when deleting rules.
* This fix has been suggested for SRU by jdstrand [1],
and has already been available in 21.04 and the snap.
[1] https:/
[Original Description]
UFW versions 0.35 (on Ubuntu 16.04 LTS) and 0.36 (on Ubuntu 20.04 LTS)
If a rule is inserted without specifying the protocol, it will default to both udp and tcp. If a second rule is inserted earlier in the order that specifies the protocol but is otherwise identical, UFW will delete the wrong rule if the first rule is deleted.
This is repeatable with the following script:
ufw insert 1 allow from 1.1.1.1/26 to any port 22
ufw insert 2 allow from 1.2.3.4/26 to any port 22
ufw insert 1 allow from 1.2.3.4/26 to any port 22 proto tcp
iptables -L -n | grep -A 6 "Chain ufw-user-input"
yes | ufw delete 3
iptables -L -n | grep -A 4 "Chain ufw-user-input"
The output is as follows:
Chain ufw-user-input (1 references)
target prot opt source destination
ACCEPT tcp -- 1.2.3.0/26 0.0.0.0/0 tcp dpt:22
ACCEPT tcp -- 1.1.1.0/26 0.0.0.0/0 tcp dpt:22
ACCEPT udp -- 1.1.1.0/26 0.0.0.0/0 udp dpt:22
ACCEPT tcp -- 1.2.3.0/26 0.0.0.0/0 tcp dpt:22
ACCEPT udp -- 1.2.3.0/26 0.0.0.0/0 udp dpt:22
Chain ufw-user-input (1 references)
target prot opt source destination
ACCEPT tcp -- 1.1.1.0/26 0.0.0.0/0 tcp dpt:22
ACCEPT udp -- 1.1.1.0/26 0.0.0.0/0 udp dpt:22
ACCEPT tcp -- 1.2.3.0/26 0.0.0.0/0 tcp dpt:22
UFW deleted the first rule for 1.2.3.0 and then the last rule for 1.2.3.0, leaving the wrong rule remaining. Here is the ufw status:
To Action From
-- ------ ----
22/tcp ALLOW 1.2.3.0/26
22 ALLOW 1.1.1.0/26
Mixing ALLOW and REJECT/DENY rules can further result in incorrect behavior due to this incorrect reordering. On port 22, this could render SSH remotely inaccessible.
For example, if one had initially set up the following rule to port 22 (TCP and UDP)...
ufw insert 1 allow from 1.2.3.4 to any port 22
...and later wanted to further restrict it to only TCP, while explicitly rejecting any other port 22 connections...
ufw insert 1 allow from 1.2.3.4 to any port 22 proto tcp
ufw insert 2 reject from any to any port 22
yes | ufw delete 3
...this would result in SSH becoming inaccessible.
Instead if one had the initial configuration...
ufw insert 1 reject from 1.0.0.0/8 to any port 22
ufw insert 2 allow from any to any port 22
...which was later updated to be...
ufw insert 1 reject from 1.0.0.0/8 to any port 22 proto tcp
ufw insert 2 allow from any to any port 22 proto tcp
yes | ufw delete 3
...this would result in 1.0.0.0/8 incorrectly being allowed to access port 22. While this is a contrived scenario, it is possible and reproducible.
A reboot is required to fix the issue, as it reloads the configuration to the expected order.
description: | updated |
description: | updated |
description: | updated |
information type: | Public → Private Security |
Changed in ufw (Ubuntu): | |
status: | New → In Progress |
assignee: | nobody → Jamie Strandboge (jdstrand) |
tags: | added: seg sts-sponsor-mfo |
Changed in ufw (Ubuntu Bionic): | |
status: | New → In Progress |
importance: | Undecided → Medium |
assignee: | nobody → Mauricio Faria de Oliveira (mfo) |
Changed in ufw (Ubuntu Focal): | |
status: | New → In Progress |
importance: | Undecided → Medium |
assignee: | nobody → Mauricio Faria de Oliveira (mfo) |
Changed in ufw (Ubuntu Hirsute): | |
status: | New → In Progress |
importance: | Undecided → Medium |
assignee: | nobody → Mauricio Faria de Oliveira (mfo) |
description: | updated |
This bug should probably be upgraded to a security issue, as anyone relying on specific ordering combining explicit ALLOW with explicit REJECT/DROP might find either the wrong ports closed or the wrong ports unexpectedly open.