Kevin BeaumontCitrix Netscaler customers - keep calm and patch CVE-2025-5777 from Tuesday.
It allows unauth memory reads, has similarities to CitrixBleed (CVE-2023-4966) as may allow session token theft.
An update on CVE-2025-5777, explaining why orgs should identify systems and patch.
https://doublepulsar.com/citrixbleed-2-electric-boogaloo-cve-2025-5777-c7f5e349d206
Worth noting that every write up says this vuln applies to the management interface - but that isn’t true, it’s because the initial CVE entry was wrong, and nobody does CVE entry updates in write ups.
A bit more on this. https://www.theregister.com/2025/06/24/critical_citrix_bug_citrixbleed/
Citrix on this one:
"At this time, there have been no reports or indications that the vulnerabilities described in CTX693420 (CVE-2025-5349 and CVE-2025-5777) are being actively exploited in the wild. However, due to the critical severity of these issues (CVSS scores of 8.7 and 9.3), We strongly recommends that affected customers apply the updated patches immediately to mitigate any potential risks."
NHS Digital's cyber alert database has been updated too. https://digital.nhs.uk/cyber-alerts/2025/cc-4670
I highly recommend bookmarking this site for the alerts, they're really good at filtering noise:
https://digital.nhs.uk/cyber-alerts
E.g. if you select 'high' category, there's only one a month on average
ReliaQuest are reporting with medium confidence that CitrixBleed2, Electric Boogaloo, is being exploited in the wild HT @CyberLeech https://reliaquest.com/blog/threat-spotlight-citrix-bleed-2-vulnerability-in-netscaler-adc-gateway-devices/
My view on that is I don’t have the data to back it up (because Citrix haven’t provided any way to identify exploitation, including to customers), but if true and the threat actor is running those tools with that provider, it’s probably a ransomware group again.
Citrix blog on CVE-2025-5777 and some other ones https://www.netscaler.com/blog/news/netscaler-critical-security-updates-for-cve-2025-6543-and-cve-2025-5777/
NetScaler Critical Security Updates for CVE-2025-6543 and CVE-2025-5777
Over the past two weeks, Cloud Software Group has released builds to address CVE-2025-6543 and CVE 2025-5777, which affect NetScaler ADC and NetScaler Gateway if they are configured as a Gateway (VPN virtual server, ICA Proxy, CVPN, RDP Proxy) OR an Authentication Authorization and Auditing (“AAA”) virtual server. While both of the vulnerabilities involve the same modules, the exposures differ. CVE 2025-6543, if exploited, could lead to a memory overflow vulnerability, resulting in unintended control flow and Denial of Service. CVE 2025-5777 arises from insufficient input validation that leads to memory overread.
If you see this GitHub PoC for CVE-2025-5777 doing the rounds:
https://github.com/mingshenhk/CitrixBleed-2-CVE-2025-5777-PoC-
It’s not for CVE-2025-5777. It’s AI generated. The links in the README still have ChatGPT UTM sources.
The PoC itself is for a vuln addressed in 2023 - ChatGPT has hallucinated (made up) the cause of the vuln using an old BishopFox write up of the other vuln.
I’ve heard that Citrix are complaining me billing this CitrixBleed 2 is causing them reputational damage, and isn’t related in any way to CitrixBleed.
For the record - it was a dumb joke name to attraction attention for patching. I know it isn’t exactly the same cause.
But, ya know, it is a memory disclosure vuln which reveals sensitive info, and it does require ICA sessions be reset.. which only happened before with CitrixBleed.
I expect technical details of CVE-2025-5777 exploitation to become available next week.
Further suggestions CVE-2025-5777 details will release next week. https://xcancel.com/Horizon3Attack/status/1940879804221522279 via https://horizon3.ai
I've published my scan in progress of CVE-2025-5777 patching status, listing IPs, hostnames, Citrix Netscaler build numbers and if they're vulnerable to CitrixBleed2.
The scan isn't finished yet so these are only about a quarter of the results - unfortunately my coding skills are shite and it's really slow - should be finished over weekend or early next week.
Also, the SSL certificate hostnames are separated by comma which throws out CSV - sorry, I'll fix that later.
If anybody is wondering btw it's 4047 definitely vulnerable (so far) from 17021 scanned instances - so 24% unpatched after about 3 weeks.
But scan is still running obvs so the vuln number will keep growing.
If anybody likes stats
- Of the 42 identified NHS Netscalers so far, 37 are patched🥳 The NHS are really good at this nowadays.
- Of the 65 identified .gov.uk Netscalers so far, only 48 are patched 😅 All of the unpatched are councils, which are obviously severely budget constrained in many cases - I'm also not sure they actually know they're supposed to be patching.
First exploitation details for CVE-2025-5777 - the Netscaler vuln - are out. https://labs.watchtowr.com/how-much-more-must-we-bleed-citrix-netscaler-memory-disclosure-citrixbleed-2-cve-2025-5777/
If you call the login page, it leaks memory in the response 🤣
I don’t want to specify too much extra technical info on this yet - but if you keep leaking the memory via requests, there’s a way to reestablish existing ICA sessions from the leaked memory.
Updated scan results for CVE-2025-5777: https://github.com/GossiTheDog/scanning/blob/main/CVE-2025-5777-CitrixBleed2-ElectricBoogaloo-patching.txt
It's still partial due to bugs, but about 18k servers.
CVE-2025-5777 is under active exploitation, since before the WatchTowr blog.
CVE-2025-5777 (Citrix Netscaler vuln) has been under active exploitation since mid June, with people dumping memory and using this to try to access sessions.
TTPs to hunt for:
- In Netscaler logs, repeated POST requests to *doAuthentication* - each one yields 126 bytes of RAM
- In Netscaler logs, requests to doAuthentication.do with "Content-Length: 5"
- In Netscaler user logs, lines with *LOGOFF* and user = "*#*" (i.e. # symbol in the username). RAM is played into the wrong field.
Horizon3 have a good write up here, I don't think they were aware this is already being exploited for almost a month: https://horizon3.ai/attack-research/attack-blogs/cve-2025-5777-citrixbleed-2-write-up-maybe/
Worth noting I was only able to find exploitation activity due to the WatchTowr and Horizon3 write ups - Citrix support wouldn't disclose any IOCs and incorrectly claimed (again - happened with CitrixBleed) that no exploitation in the wild. Citrix have gotta get better at this, they're harming customers.
Just to be super clear, although Citrix claim that CitrixBleed 2 is in no way related to CitrixBleed, it allows direct session token theft - Citrix are wrong. Horizon3 have the POC and it's already being exploited - Citrix were also wrong.
"Not the most novel thing in the world… but this is much much worse than it initially appears. Take a look at the following video where you’ll see that it’s possible to receive legitimate user session tokens via this vector. "
Exploitation IOCs for CVE-2025-5777 aka CitrixBleed 2, these are actively stealing sessions to bypass MFA for almost a month. Some are also doing Netscaler fingerprint scanning first.
64.176.50.109
139.162.47.194
38.154.237.100
38.180.148.215
102.129.235.108
121.237.80.241
45.135.232.2
HT @ntkramer and the folks at @greynoise
Look for lots of connections to your Netscaler devices over past 30 days. More IPs coming as also under mass exploitation. More IPs: https://viz.greynoise.io/tags/citrixbleed-2-cve-2025-5777-attempt?days=30
More from @greynoise telemetry - they now push CVE-2025-5777 (CitrixBleed 2) exploitation to June 23rd. I can push it back further, blog incoming.
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
There’s 7 more IPs on GreyNoise exploiting CitrixBleed 2 today, all marked as malicious. https://viz.greynoise.io/query/tags:%22CitrixBleed%202%20CVE-2025-5777%20Attempt%22%20last_seen:90d
“Citrix declined to say if it's aware of active exploitation”
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.
CISA have modified the CVE-2025-5777 entry to link to my blog 🙌 I’m hoping this gets more visibility as a bunch of us can see from Netflow ongoing threat actor Netscaler sessions to.. sensitive orgs.
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.
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
Updated CitrixBleed2 scan results of vuln/not vuln
https://github.com/GossiTheDog/scanning/blob/main/CVE-2025-5777-CitrixBleed2-ElectricBoogaloo-patching.txt
https://github.com/GossiTheDog/scanning/blob/main/CVE-2025-5777-CitrixBleed2-ElectricBoogaloo-patching.txt
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
CISA orders agencies to immediately patch Citrix Bleed 2, saying bug poses ‘unacceptable risk’
The one-day deadline issued by CISA on Thursday appears to be the shortest one ever issued. Federal civilian agencies are typically given three weeks to patch bugs added to the known exploited vulnerability catalog.
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.
If you ask Citrix support for IOCs for CVE-2025-5777 and they send you a script to run that looks for .php files - they’ve sent you an unrelated script, which has nothing to do with session hijacking or memory overread.
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.
M Schommer@GossiTheDog
So… could there possibly exist another Citrix 0day that this script looks for?
Right script, different CVE? :D
So… could there possibly exist another Citrix 0day that this script looks for?
Right script, different CVE? :D
gmmds@musevg @GossiTheDog Well we haven’t seen anything yet about 2025-6543… and that was supposed to be the scary one!
Chad Brigance@GossiTheDog this one is for CVE-2025-6543
@definity yea, support are getting confused and sending that one for CVE-2025-5777
tehfishman@GossiTheDog @definity going to buy stock in clown makeup before the news reports the sudden spike in demand.
Darses@GossiTheDog Looks like the two-digit billion dollar corp that closed my report as "informative, we don't see the issue here" still hasn't updated yet.
Mr_K@GossiTheDog is this scan still running or has it now completed?
João Tiago Rebelo (NAFO J-121)@GossiTheDog #Alt4You #AltText two screen captures from Citrix website, the other one from Akamai website. The first one says:
"Can I fix these vulnerabilities using Web Application Firewall signatures?
No, it is not possible to fix the vulnerabilities with Web Application Firewall signatures.
The second one, posted later, says:
"App & API Protector mitigation
In response to CitrixBleed 2, the WAF Threat Research Team released a new Rapid Rule on July 7, 2025, with a default action set to "Alert":
- 3000967-Citrix NetScaler Memory Disclosure Detected (CVE-2025-5777)".
"Can I fix these vulnerabilities using Web Application Firewall signatures?
No, it is not possible to fix the vulnerabilities with Web Application Firewall signatures.
The second one, posted later, says:
"App & API Protector mitigation
In response to CitrixBleed 2, the WAF Threat Research Team released a new Rapid Rule on July 7, 2025, with a default action set to "Alert":
- 3000967-Citrix NetScaler Memory Disclosure Detected (CVE-2025-5777)".
@jt_rebelo @GossiTheDog The second one isn’t Citrix - that’s Akamai.
@gmmds thanks, corrected. @GossiTheDog
@GossiTheDog The great thing about "as far as I know"/"not as far as I know" class statements, unlike almost all other types of statements, is that you can increase their accuracy through the easy work of knowing less rather than the arduous task of knowing more.
It's epistemology's any% speedrun strat.
Steve Scott@GossiTheDog this feels very much like a corp Comms team in crisis management mode, thinking obfuscation will make the situation better. It's a natural reaction, but not one that helps mitigation.
A brutally honest 'we screwed up, here is what we can share without making the situation worse' along with some willingness to offer hotfixes rather than full releases is the better path forward.
On the plus side, I did get to read their latest Tolly report for lolz
Wouter Hindriks@GossiTheDog How are you monitoring this traffic? I remember you making a similar statement on the Ingram Micro case.
Long Shot@GossiTheDog They must be thinking it is gossip...
Chilly 
🛡️ 
Phil@GossiTheDog Congratulations
Emory@GossiTheDog oh my g-d they did it again
@GossiTheDog Obviously this is a Ripley Protocol type of situation; but is it known how long the session cookies would be expected to remain valid if not explicitly purged? Configurable and wide variation in plausible values? Life of connection until manual or enforced disconnect? Fixed or very likely default number of minutes after successful authentication?
CatButtes 
@GossiTheDog does anybody hear that statement and think anything other than “Citrix is aware that there is widespread, active exploitation. They just don’t want to admit it because it makes them look bad”?
@catbuttes @GossiTheDog but that's the beauty of it - they don't SAY it, so they legally don't admit to it, and everything else, however silly or dirty, is third party conjecture which doesn't matter in court 🤔
jaKa Močnik@GossiTheDog well, they already stated it in the sentence above. :D
TheTomas@GossiTheDog First Victims in Switzerland and Germany
@TheTomas I don't see any evidence either of those are CitrixBleed2 caused, for what it's worth. One appears to be a power outage, the other has an unpatched Netscaler but it's still online
Jérôme Meyer@GossiTheDog I had a look at network traffic from today and some of them are proxy exit nodes; some do broad IoT scanning.
Two of them really stick out as they seem to exclusively target Citrix endpoints: 78.128.113.30 and 38.54.59.96
@jmeyer worth running these too:
Kevin Beaumont (@GossiTheDog@cyberplace.social)
Exploitation IOCs for CVE-2025-5777 aka CitrixBleed 2, these are actively stealing sessions to bypass MFA for almost a month. Some are also doing Netscaler fingerprint scanning first. 64.176.50.109 139.162.47.194 38.154.237.100 38.180.148.215 102.129.235.108 121.237.80.241 45.135.232.2 HT @ntkramer@infosec.exchange and the folks at @greynoise@infosec.exchange Look for lots of connections to your Netscaler devices over past 30 days. More IPs coming as also under mass exploitation. More IPs: https://viz.greynoise.io/tags/citrixbleed-2-cve-2025-5777-attempt?days=30
@GossiTheDog 38.154.237.100 is a definite yes (I looked at past 24h)
Ketumbra@GossiTheDog "I wrote this vuln back on June 24th..."
Pretty sure that's not what you meant ;)
Pretty sure that's not what you meant ;)
@ketumbra lols, good spot - fixed
JJ@GossiTheDog Thanks so much for this info and for all the info provided prior to this. I was able to confirm with our Citrix team two weeks ago that we were patched already, and I'm just getting emails this week from higher ups to look into this, so I'm very much ahead of the game.
Aside from social media, is there anywhere you suggest keeping an eye on daily for vulnerability info?
Martin S 🚩❤️✊ 🇵🇸🇺🇦
Lowlands@GossiTheDog seeing the first hits from one of the mentioned IPs on 6/20.
@lowlands which IP?
@GossiTheDog 64[.]176[.]50[.]109
@lowlands ah yep. They did fingerprinting of Netscaler firmware versions, then exploited unpatched boxes afterwards
@GossiTheDog @ntkramer @greynoise
My own honeypot only sees activity from Private VPN. No fingerprinting first. Most POST /p/u/doAuthentication.do, some POST /nf/auth/doAuthentication.do. User-Agent: "Vuln3rableVuln3rable..."
2025-07-07
190.60.16.26
103.27.203.82
45.9.249.58
185.94.192.162
128.1.160.146
200.110.153.22
2025-07-06
193.37.253.202
200.110.153.22
217.138.222.66
82.221.113.209
80.239.140.197
@GossiTheDog was CitrixBleed the one that Citrix issued a patch for that didn't actually fix the vulnerability in like Nov 2023?
meriksson@GossiTheDog Great artwork as always.
husjon.dev@GossiTheDog I'm glad to see my image contribution is still going strong with new iterations 😅
(original: https://fosstodon.org/@husjon/111308387657992171)
(original: https://fosstodon.org/@husjon/111308387657992171)
@husjon I owe you a beer