CVE-2026-6985Public exploitNetwork attack vector

Unauthenticated service hang via zero-length TCP option

Published Apr 25, 2026 · Updated Apr 25, 2026

Infinite loop in Cesanta Mongoose 7.0 through 7.20 allows remote attackers to hang its event loop with a malformed TCP option. In net_builtin.c, handle_opt reads an untrusted optlen byte and advances both the option pointer and remaining length by zero, so its loop never progresses. The built-in TCP/IP stack must be enabled; one unauthenticated SYN can stop connections and timers until a watchdog or device reset restores service.

CVSS severity5.3
Medium
EPSS probability0.56%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Infinite loop in Cesanta Mongoose 7.0 through 7.20 allows remote attackers to hang its event loop with a malformed TCP option. In net_builtin.c, handle_opt reads an untrusted optlen byte and advances both the option pointer and remaining length by zero, so its loop never progresses. The built-in TCP/IP stack must be enabled; one unauthenticated SYN can stop connections and timers until a watchdog or device reset restores service.

The record

CVE
CVE-2026-6985
Published
Apr 25, 2026
Updated
Apr 25, 2026
Vendor
Cesanta
Product
Mongoose
Classifications
CWE-404, CWE-835, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 25, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 25, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=7.0
  2. Affected versionversion=7.1
  3. Affected versionversion=7.10
  4. Affected versionversion=7.11
  5. Affected versionversion=7.12
  6. Affected versionversion=7.13
  7. Affected versionversion=7.14
  8. Affected versionversion=7.15
  9. Affected versionversion=7.16
  10. Affected versionversion=7.17
  11. Affected versionversion=7.18
  12. Affected versionversion=7.19
  13. Affected versionversion=7.2
  14. Affected versionversion=7.20
  15. Affected versionversion=7.3
  16. Affected versionversion=7.4
  17. Affected versionversion=7.5
  18. Affected versionversion=7.6
  19. Affected versionversion=7.7
  20. Affected versionversion=7.8
  21. Affected versionversion=7.9

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Cesanta · Mongooseversion=7.0; version=7.1; version=7.10; version=7.11; version=7.12; version=7.13; version=7.14; version=7.15; version=7.16; version=7.17; version=7.18; version=7.19; version=7.2; version=7.20; version=7.3; version=7.4; version=7.5; version=7.6; version=7.7; version=7.8; version=7.9

Published CVSS scores

5.5VulDBCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P
5.3VulDBCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0VulDBAV:N/AC:L/Au:N/C:N/I:N/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-404Improper Resource Shutdown or Release
CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
T1499.004Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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