CVE-2026-6985 Details
Description
A weakness has been identified in Cesanta Mongoose up to 7.20. This vulnerability affects the function handle_opt of the file /src/net_builtin.c of the component TCP Option Handler. This manipulation of the argument optlen causes infinite loop. The attack is possible to be carried out remotely. The exploit has been made available to the public and could be used for attacks. Upgrading to version 7.21 is able to resolve this issue. Upgrading the affected component is advised. VulDB has contacted the vendor early and they confirmed quickly, that this issue got fixed already.
A denial-of-service vulnerability has been identified in Cesanta Mongoose versions prior to 7.21. The issue arises in the TCP Option Handler within the `handle_opt` function of the file `/src/net_builtin.c`. The vulnerability is caused by a missing validation of the `optlen` field in TCP options. When `optlen` is set to zero, the function enters an infinite loop, effectively freezing the Mongoose event loop. This issue can be exploited remotely with a single unauthenticated TCP SYN packet that includes a malformed option. The vulnerability has been publicly disclosed and is known to be exploitable.
Upgrading to Cesanta Mongoose version 7.21 or later resolves this vulnerability.
Metrics
CVSS 4.0 Severity and Vector Strings:
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed Apr 27, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://github.com/cesanta/mongoose/releases/tag/7.21 | [email protected] | ProductRelease Notes |
| https://github.com/dwBruijn/CVEs/blob/main/Mongoose/TCP_opt_dos.md | [email protected] | ExploitThird Party Advisory |
| https://vuldb.com/submit/796230 | [email protected] | Third Party AdvisoryVDB Entry |
| https://vuldb.com/vuln/359528 | [email protected] | Third Party AdvisoryVDB Entry |
| https://vuldb.com/vuln/359528/cti | [email protected] | Permissions RequiredVDB Entry |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-404 | Improper Resource Shutdown or Release | [email protected] |
| CWE-835 | Loop with Unreachable Exit Condition ('Infinite Loop') | [email protected] |
Affected Products
| Product | Versions |
|---|---|
| cesanta mongoose | >= 7.0, < 7.21 |
CPE
Remediation
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Change History
4 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Jun 17, 2026 | CVE Modified | [email protected] |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| Apr 29, 2026 | Initial Analysis | [email protected] |
| Apr 25, 2026 | New CVE Received | [email protected] |