CVE-2026-97701
Zulip: Missing content-length limit on POST /messages/render allows denial-of-service via oversized requests
Zulip is an open-source team collaboration tool. In Zulip Server versions through 12.1, the authenticated POST /messages/render endpoint renders the content parameter without enforcing the normal message length limit used by message send and edit operations. An authenticated user can submit Markdown up to the server body-size limit, causing disproportionate backend CPU consumption, and repeated or concurrent requests can degrade Markdown rendering performance or backend availability for other users. This issue is fixed in version 12.2.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- Low
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- None
- Availability
- High
Exploit likelihood
What each source reports
CVE List Score used
Zulip: Missing content-length limit on POST /messages/render allows denial-of-service via oversized requests
Zulip is an open-source team collaboration tool. In Zulip Server versions through 12.1, the authenticated POST /messages/render endpoint renders the content parameter without enforcing the normal message length limit used by message send and edit operations. An authenticated user can submit Markdown up to the server body-size limit, causing disproportionate backend CPU consumption, and repeated or concurrent requests can degrade Markdown rendering performance or backend availability for other users. This issue is fixed in version 12.2.
- Record
CVE-2026-97701- CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H - Weakness
- CWE-770
- Updated
- 2026-11-04
EUVDEUVD-2026-117032
Zulip is an open-source team collaboration tool. In Zulip Server versions through 12.1, the authenticated POST /messages/render endpoint renders the content parameter without enforcing the normal message length limit used by message send and edit operations. An authenticated user can submit Markdown up to the server body-size limit, causing disproportionate backend CPU consumption, and repeated or concurrent requests can degrade Markdown rendering performance or backend availability for other users. This issue is fixed in version 12.2.
- Record
EUVD-2026-117032- CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H - Updated
- 2026-11-04
NVD
Zulip is an open-source team collaboration tool. In Zulip Server versions through 12.1, the authenticated POST /messages/render endpoint renders the content parameter without enforcing the normal message length limit used by message send and edit operations. An authenticated user can submit Markdown up to the server body-size limit, causing disproportionate backend CPU consumption, and repeated or concurrent requests can degrade Markdown rendering performance or backend availability for other users. This issue is fixed in version 12.2.
- Record
CVE-2026-97701- CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H - Weakness
- CWE-770
- Updated
- 2026-11-07
OSV
Zulip: Missing content-length limit on POST /messages/render allows denial-of-service via oversized requests
Zulip is an open-source team collaboration tool. In Zulip Server versions through 12.1, the authenticated POST /messages/render endpoint renders the content parameter without enforcing the normal message length limit used by message send and edit operations. An authenticated user can submit Markdown up to the server body-size limit, causing disproportionate backend CPU consumption, and repeated or concurrent requests can degrade Markdown rendering performance or backend availability for other users. This issue is fixed in version 12.2.
- Record
CVE-2026-97701- CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H - Weakness
- CWE-770
- Updated
- 2026-11-05
Affected products
History
| Recorded | Changed | Sources |
|---|---|---|
| aliases, references | EUVD, NVD, OSV | |
| cwes, references, severity, title | CVE List, NVD | |
| first indexed | EUVD |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2026-97701 is a medium vulnerability (CVSS 6.5) in Zulip, published November 4, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.43%, the 37th percentile. No source names a fixed version.
References
github.com/zulip/zulip/security/advisories/GHSA-m257-w4r5-5rmf
zulip.readthedocs.io/en/latest/overview/changelog.html
nvd.nist.gov/vuln/detail/CVE-2026-97701