Why Correct Firewall Timeout Configuration Is Important
Sitting at my desk in the mornings — third coffee in hand — I’m always seized with how a simple firewall timeout can be the difference between a fortified network and an open door to any attacker.
Sanjay Seth here from P J Networks Pvt Ltd. I am an early bird in this game, having started in 1993. I started out as a network admin when we were still wrangling voice and data through PSTN muxes; Yes, we were dinosaurs. Saw the Slammer worm wreak havoc on global networks firsthand, and after that I’ve been riding the roller coaster that is security, or crashing into it. These days, I own my own shop, consulting clients (most recently three banks) on upgrading their zero-trust architectures. Still buzzing from DefCon’s hardware hacking village—which reminds that security is not just about software, but all the minutae of protocol including timeout values.
So the long and the short of it is this: firewall session timeouts are the unsung heroes of your network stack. Misconfigure them, and you might as well be giving your keys to hackers. Let me explain—you know, from actual scars and victories.
The Role of Timeouts
If you think firewalls simply block or allow traffic, it’s only half the story. Firewalls use sessions — they know who spoke to whom, about what, and for how long. Session timeout indicates to your firewall when to stop remembering that connection.
Why’s that important? Think about it like a car lot where every buyer just left their cars unlocked for the rest of time. Session timeouts are like those security guards who pop in every few minutes to check whether you still want that car unlocked. Without them — well, anybody who walks by can just jump in.
Since the early days I witnessed the kind of legacy networks where they presumed sessions could last for hours or days (think voice/data setups such as PSTN muxes), But times have changed—applications have gotten faster, attackers have gotten craftier.
Timeouts ensure:
- Automatic closure of idle connections
- Resources aren’t wasted
- Session hijacking risk is reduced
But set them too short, and you piss off users with dropped connections. Too short, and you risk disaster.
Risks of Long Sessions
Here’s a hard fact: long session timeouts are a hacker’s paradise.
I’ve seen companies with session timeouts in hours (seriously), thinking, “It’s better to keep the session alive for usability.” That’s like keeping your front door wide open because you don’t want to mess with keys every time you go out.
Long sessions can:
- Compromise idle sessions with no re-authentication required
- Blow up your exposure window for Man-in-the-Middle (MitM) attacks
- Waste firewall memory and slow down performance (no one seems to discuss this but I notice)
The one case where I assisted a client that had endured session hijacking attacks because their firewall was retaining TCP sessions beyond 4 & ½ hrs. Hackers took advantage of these idle moments, injecting commands as if they were real users. The lesson: The network’s biggest weakness wasn’t software bugs — it was timeout misconfigurations.
And don’t get me started about automatic reconnects that occasionally get handled by some applications. If your timeout is too lenient, attackers can take advantage of those residual sessions and access them without proper authorization.
Configuring Proper Values
When it comes to policies, however, the devil is in the details and here’s where a lot of admins (I’m guilty) get lazy or simply default to copy-pasting recommendations that don’t apply to their environment.
Determining timeouts is more art than science, combined with an understanding of your traffic patterns. Here’s what I always start with:
- TCP sessions: 5–15 minutes of inactivity
- UDP sessions: Often shorter, 30–60 seconds (it’s stateless, and you don’t want your firewall to remember until the end of time)
- DNS or HTTP sessions: even less — 30 seconds to 2 minutes
But here’s the kicker: this very behavior differs from vendor to vendor. (Timeout) not the same as on Fortinet or Palo Alto firewall. Know your gear.
A quick tip when configuring:
- Look at your logs first. Determine average time spent in session and average time spent idle
- Avoid relying on best practice sheets from your vendor. Customize.
- Sync timeouts with your zero trust policies — if the user’s context changes (device, location, etc.) sessions should expire quickly
And if you haven’t taken another look at those rules in the last 6–12 months, you’re falling behind. Unlike your old dial-up modem, session timeout policies aren’t “set it and forget it.”
Monitoring User Sessions
You cannot protect what you’re unaware of. That’s why tracking session activity is essential.
In P J Networks we deploy solutions that help clients:
- Monitor ongoing sessions and length of time each of them lasted
- Notify when sessions above thresholds
- Identify abnormalities like multiple reconnect or prolonged idle time
Here’s where logs are your best friend — but also your worst nightmare, if you don’t have the right tools. Manually sorting entries is a futility similar to looking for a dropped bolt in a hardware hacking village (Hello DefCon).
With automated monitoring associated with your SIEM or firewall management consoles, all of this becomes manageable. Otherwise you’re flying blind.
Reducing Idle Connections
So, idle connections—man, those are the stealthy beasts draining network resources and presenting open windows for attacks.
Here are ways you can reduce idle timeouts and improve session security (from my past experiences):
- User education: Explain to your users that having long-lived idle connections is pointless, and probably insecure — this isn’t dial-up anymore.
- Application-side controls: Motivate development teams to implement session heartbeat controls that work to close idle sessions.
- Firewall clean up policies: Enable aggressive session aging for out-of-the-norm traffic or uncommon protocols.
- Periodic session reset: For high-risk assets, configure firewalls to proactively reset sessions during off-peak times (e.g., midnight).
- Watch out for VPN timeouts: A lot of big networks degenerate around VPN session timeouts, and that’s just pathetic. VPNs should terminate immediately, except when an active user is present.
Quick Take
It’s not trivial that your firewall timeout settings. They’re security controls.
- Lengthy session timeouts = gateway to hijacking and persistent threats.
- Adjust timeout values according to real network and app behavior.
- Watching sessions all day, every day, and catching problems before the bad guys do.
- The best part is that reducing idle connections is a low-tech, high-impact approach to hardening your perimeter.
Closing Thoughts
Now, I’m the first to admit I’ve bungled timeout calls during my career. (Once left a timeout at eight hours — yes, eight — and learned the hard way when a client’s network was breached). But lessons are valuable. And the picture continues to change.
After spending the last few weeks with three banks enhancing their zero-trust models, I can tell you this much — every. single. firewall. timeout. setting. was double-checked. because zero-trust is more than a buzzword, it’s about shattering assumptions, including the assumption of how long a session should live.
In my opinion, firewall session management deserves more than some time in the limelight. These days people are pursuing high-falutin’ AI driven solutions and cloud sorcery — but genuinely the fundamentals become paramount. (And to be honest, I am somewhat dubious towards most AI-powered buzzwords — just give me actual configuration and monitoring over hype any day).
So the next time you are having your coffee, go and check your firewall sessions. Those timeout settings could save your network’s day — or well, ruin it.
Stay safe, and ping me if you just want to chat firewalls, servers, or routers.
Sanjay Seth
CyberSecurity Consultant, P J Networks Pvt Ltd since 1993.
Still coffee’d up and loving security—one config at a time.