CVE-2021-43799: RabbitMQ exposes ports with weak default secrets in Zulip Server
Noroxi assessment
Priority: Plan (action score 41/100)
- Public proof-of-concept code exists (GitHub); there is no record of exploitation in the wild.
- Probability of exploitation in the next 30 days: 5.3% (FIRST EPSS); higher than 92.6% of all records.
- Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
- According to CISA the attack is automatable: targets can be found by mass scanning.
- No fixed version is recorded, but the references include a patch (commit or PR) link.
Add it to your regular patch cycle. See the fix and affected versions sections below.
Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it
Primary sources: NVD · CVE.org · FIRST EPSS
Zulip is an open-source team collaboration tool. Zulip Server installs RabbitMQ for internal message passing. In versions of Zulip Server prior to 4.9, the initial installation (until first reboot, or restart of RabbitMQ) does not successfully limit the default ports which RabbitMQ opens; this includes port 25672, the RabbitMQ distribution port, which is used as a management port. RabbitMQ's default "cookie" which protects this port is generated using a weak PRNG, which limits the entropy of the password to at most 36 bits; in practicality, the seed for the randomizer is biased, resulting in approximately 20 bits of entropy. If other firewalls (at the OS or network level) do not protect port 25672, a remote attacker can brute-force the 20 bits of entropy in the "cookie" and leverage it for arbitrary execution of code as the rabbitmq user. They can also read all data which is sent through RabbitMQ, which includes all message traffic sent by users. Version 4.9 contains a patch for this vulnerability. As a workaround, ensure that firewalls prevent access to ports 5672 and 25672 from outside the Zulip server.
- Published
- Jan 25, 2022
- Updated
- Jun 17, 2026
- EPSS
- 5.3% · 92th percentile
- CWE
- CWE-338
Report tools
Action score
41
Plan
Add it to your regular patch cycle.
- CVSS
- 39 / 40 · 9.8 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 2 / 30 · 5.3%
CISA SSVC decision
- Exploitation
- none
- Automatable
- yes
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- 9.8
- CNA · GitHub_M
- 8.6
- 1.2 point gap
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Get told when this record changes
- Not in KEV: no record of exploitation in the wild
- Proof of concept exists, no weaponized module
- No fixed version yet
If any of these changes, we'll tell you in the daily email digest.
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Noroxi analysis
What does it mean in your environment?
The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.
We use this product, ask for helpAffected systems
Is your version affected?
Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.
| Vendor | Product | CPE |
|---|---|---|
| zulip | zulip | cpe:2.3:a:zulip:zulip |
Affected versions
NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.
- zulip zulipbefore 4.9
Versions reported by the vendor
Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.
zulip zulip
- < 4.9affected
Same product
zulip: all recordsOther highest-scoring records for the same primary product.
- CVE-2026-102893Zulip: OpenID Connect authentication ignores the email_verified claim36Monitor
- CVE-2022-31168Zulip Server insufficient authorization for changing bot roles35Monitor
- CVE-2021-3967Improper Access Control in zulip/zulip35Monitor
Published before and after this one in the same product
- ← EarlierCVE-2021-43791Dec 1, 2021 · Ineffective expiration validation for invitation links in Zulip21Monitor
- ← EarlierCVE-2021-3866Jan 20, 2022 · Cross-site Scripting (XSS) - Stored in zulip/zulip21Monitor
- Later →CVE-2022-24751Mar 16, 2022 · Race condition in Zulip29Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
No fix version is recorded for this entry. Check the references for vendor advisories.
Exploit status
Proof of concept available
A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.
Evidence
- Proof-of-concept repository on GitHub ×1
Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.
| Source | Kind | Date |
|---|---|---|
| Proof-of-concept repository on GitHub | stars:1 | 2021-12-08 |
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
- First PoC-49 d
- Published
- TodayNov 2, 2026+1742 d
No history yet (it accumulates with the daily EPSS job).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
—
Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- No special conditions are required; it is repeatable.
If successful
- Confidentiality
- high · data can be read
- Integrity
- high · data or configuration can be modified
- Availability
- high · the service can be disrupted
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- High
- Availability impact
- High
Weakness class (CWE)
CWE-338 · Use of Cryptographically Weak Pseudo-Random Number Generator (PRNG)CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
nvd-primary
Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
MITRE has no CAPEC/ATT&CK mapping for this CWE.
Change log
No changes recorded on tracked fields yet. Score, KEV, exploit maturity and fix status changes appear here.
References
Show all references (3 more)Show less
Vendor advisories and official records. Exploit/PoC links are deliberately left out.