I wrote up a thing on how to hunt for CitrixBleed 2 exploitation

https://doublepulsar.com/citrixbleed-2-exploitation-started-mid-june-how-to-spot-it-f3106392aa71

“Citrix declined to say if it's aware of active exploitation”

It is aware. https://arstechnica.com/security/2025/07/critical-citrixbleed-2-vulnerability-has-been-under-active-exploit-for-weeks/?utm_brand=arstechnica&utm_social-type=owned&utm_source=mastodon&utm_medium=social

I believe Citrix may have made a mistake in the patching instructions for CitrixBleed2 aka CVE-2025-5777.

They say to do the instructions on the left, but they appear to have missed other session types (e.g. AAA) which have session cookies that can be stolen and replayed with CitrixBleed2. On the right is the CitrixBleed1 instructions.

The net impact is, if you patched but a threat actor already took system memory, they can still reuse prior sessions.

Tell anybody you know at Citrix.

CVE-2025-5777 aka CitrixBleed 2 has been added to CISA KEV now over evidence of active exploitation.

Citrix are still declining to comment about evidence of exploitation as of writing.

https://www.cisa.gov/news-events/alerts/2025/07/10/cisa-adds-one-known-exploited-vulnerability-catalog

This is how Citrix are styling Citrix Bleed 2 btw. In the blog there’s no technical details or detection details or acknowledgement of exploitation. They also directly blame NIST for their CVE description.

From Netflow I can see active victims - including systems owned by the US federal government - so strap in to see where this goes.

Some CitrixBleed2 IOCs; this is a cluster of what appears to be China going brrr, going on for weeks.

38.154.237.100
38.54.59.96

#threatintel

CISA is giving all civilian agencies 1 day to remediate CitrixBleed 2. It is encouraging all other organisations in the US to do this too.

https://therecord.media/cisa-orders-agencies-patch-citrix-bleed-2

Set up lab of Netscalers just now & owned them.

Two learnings:

1) the default logging isn’t enough to know if you’ve been exploited. So if you’re wondering where the victims are, they don’t know they’re victims as checks will come back clean unless they increased logging before. FW logs w/ IOCs fall back option.

2) the Citrix instructions post patch to clear sessions don’t include the correct session types - ICA will just reconnect as you (threat actor) still have the valid NSC_AAAC cookie.

Updated CitrixBleed 2 scan results: https://github.com/GossiTheDog/scanning/blob/main/CVE-2025-5777-CitrixBleed2-ElectricBoogaloo-patching.txt

It's down from 24% unpatched to 17% unpatched

The results are partial still, the actual numbers still vuln will be higher.

Imperva WAF have added detection and blocking for CitrixBleed 2 this weekend.

They see it being widely sprayed across the internet today - almost 12 million requests, log4shell level.

The only major vendor I’ve seen who hasn’t added a WAF rule is Citrix - they sell a WAF upsell module for Netscaler, but failed to add detection for their own vulnerability.

Updated Citrix scan results will go on Github in a few days, I've found a bug in the scan results setup which should add ~33% more hosts when fixed.

Spoiler:

CitrixBleed 2 update.

- Citrix have finally, quietly admitted exploitation in the wild -- by not commenting to press and then editing an old blog post and not mentioning it on their security update page.

- Orgs have been under attack from threat actors in Russia and China since June

- It's now under spray and pray, wide exploitation attempts.

https://doublepulsar.com/citrixbleed-2-situation-update-everybody-already-got-owned-503c6d06da9f

Citrix Netscaler internet scan still running, it's found another 1k vulnerable instances so far - will probably update Github later today or tomorrow morning.

It looks like we're back up to 18% of boxes being still vulnerable when the new list is out. It looks like a lot of orgs are patching from my list.

New CitrixBleed 2 scan data:

https://raw.githubusercontent.com/GossiTheDog/scanning/refs/heads/main/CVE-2025-5777-CitrixBleed2-ElectricBoogaloo-patching.txt

+7000 extra hosts added this round, host list is so large you need to use the raw view to see it.

Next set of data publication likely Friday, a month since the patch became available.

3832 orgs/hosts still unpatched.

I’m fairly certain the threat actor is Chinese and they reversed the patch to make the exploit.

Citrix continue to be MIA. They still have no detection guidance for customers, and haven’t told customers the extent of the issue.

#CitrixBleed2

With the #CitrixBleed2 patch data I publish it's possible to view the history on Github for each new scan and see when hosts change from vuln to patched.

It's proving incredibly effective at getting orgs to patch. I tried private notifications via HackerOne and such for CitixBleed1 in 2023 and it took months to get orgs to patch. Putting the data public brings accountability for orgs who later get breached - so there's a rush to patch.

It's definitely interesting and may need a scale out.

Citrix have a blog out about hunting for #CitrixBleed2

https://www.netscaler.com/blog/news/evaluating-netscaler-logs-for-indicators-of-attempted-exploitation-of-cve-2025-5777/

It's what was in my earlier blog - look for invalid characters in the username field and duplicate sessions with different IPs

This bit is still incomplete in the patching instructions btw - if it's a HA pair you need to additionally reset other session types or you're still vulnerable to session hijack after patching.

I'm still trying to get Citrix to update the instructions.

The Dutch Public Prosecution Office have shut down their Citrix Netscaler and removed all internet access, Dutch media speculating CitrixBleed 2 exploitation.

https://www.techzine.eu/news/security/133163/dutch-department-of-justice-offline-after-citrix-vulnerability/

Justice minister David van Weel told MPs in a briefing that it appears the weakness had been used by third parties to access the department systems.

The justice ministry said the department had applied Citrix’s recommended patches, but these failed to fully eliminate the flaw. https://www.dutchnews.nl/2025/07/prosecution-department-goes-offline-due-to-software-weakness/

Update on the situation at The Hague and the shutdown of the Dutch Public Prosecution Service internet access, NCSC Netherlands issued an update today saying all orgs should hunt for CitrixBleed 2 activity, citing my blog.

They also advise clearing all session types, not just the ones Citrix say in their security advisory.

https://advisories.ncsc.nl/advisory?id=NCSC-2025-0196

Updated #CitrixBleed2 scans https://github.com/GossiTheDog/scanning/blob/main/CVE-2025-5777-CitrixBleed2-ElectricBoogaloo-patching.txt

Fields - IP, SSL certification hostnames, Netscaler firmware, if vulnerable to CVE-2025-5777

I've had a few orgs contest that they're not vulnerable and the scan is wrong. I've assisted each org, and in each case they've been wrong - they'd patched the wrong Netscaler, the passive HA node etc.

I might move the Dutch Public Prosecution Service (OM) Citrix Netscaler incident out to a different thread, but the latest update an hour ago from local media is that they are still without internet and remote access, and they're working on several alternatives to continue criminal trials.

I expect we're going to see a wave of Netscaler incidents over the coming months, although how many will publicly disclose is another issue - the Dutch are culturally transparent.

https://nltimes.nl/2025/07/18/dutch-prosecutor-disconnects-internal-systems-internet-vulnerability

There’s a bit more in situation at the OM on Netscaler here: https://www.volkskrant.nl/binnenland/openbaar-ministerie-mogelijk-nog-weken-afgesloten-van-internet-probeert-impact-op-rechtszaken-te-beperken~b6e19434/

The OM say they patched quickly (and my scan data backs this up - they patched around June 24th) however it appears somebody got in (or took a session cookie) before patching took place and now they’re trying to contain the situation.

I think this thread exposes something about the cybersecurity industry and org posture btw - it almost all runs on Windows and EDR telemetry, hence why there’s little info on this from vendors (Netscaler is closed box appliance - they’re flying blind) and why orgs aren’t seeing anything, they don’t know how without vendors.

I keep contacting orgs and they have no idea they are compromised or how to investigate.

#CitrixBleed2