How severe is CVE-2026-73258?

CVE-2026-73258 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.

Is CVE-2026-73258 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (38th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-73258?

CVE-2026-73258 affects Cesanta Mongoose. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2026-73258?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2026-73258 published?

CVE-2026-73258 was published on 2026-08-20 and last updated on 2026-09-29.

CVE-2026-73258

CVE-2026-73258 is a medium-severity vulnerability in Cesanta Mongoose with a CVSS 3.x base score of 6.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-697.

Key facts

Severity: Medium (CVSS 3.x base score 6.5)
EPSS exploit prediction: 0% (38th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-697
Affected product: Cesanta Mongoose
Published: 2026-08-20
Last modified: 2026-09-29

Description

Mongoose is an embedded web server and network library. Prior to 7.22, a remote attacker can place a lone carriage return or line feed in multipart input processed by mg_http_next_multipart() in src/http.c. The loops comparing s[b] and s[b + 1], and s[h2] and s[h2 + 1], use an incorrect AND condition and stop when either character resembles part of a CRLF terminator. This truncates headers, filenames, or boundaries and can cause an application to accept dangerous content after seeing a misleading Content-Type value. This issue is fixed in version 7.22.

Frequently asked questions

What is CVE-2026-73258?: Mongoose is an embedded web server and network library. Prior to 7.22, a remote attacker can place a lone carriage return or line feed in multipart input processed by mg_http_next_multipart() in src/http.c. The loops comparing s[b] and s[b + 1], and s[h2] and s[h2 + 1], use an incorrect AND condition and stop when either character resembles part of a CRLF terminator. This truncates headers, filenames, or boundaries and can cause an application to accept dangerous content after seeing a misleading Content-Type value. This issue is fixed in version 7.22.
How severe is CVE-2026-73258?: CVE-2026-73258 has a CVSS 3.x base score of 6.5, rated medium severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity low, and availability none.
Is CVE-2026-73258 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (38th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-73258?: CVE-2026-73258 affects Cesanta Mongoose. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2026-73258?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2026-73258 published?: CVE-2026-73258 was published on 2026-08-20 and last updated on 2026-09-29.

References

Affected products (1)

cpe:2.3:a:cesanta:mongoose:*:*:*:*:*:*:*:*

More vulnerabilities in Cesanta Mongoose

CVE-2022-25299 — Critical (CVSS 9.8): This affects the package cesanta/mongoose before 7.6. The unsafe handling of file names during upload using…
CVE-2020-25756 — Critical (CVSS 9.8): A buffer overflow vulnerability exists in the mg_get_http_header function in Cesanta Mongoose 6.18 due to a lack of…
CVE-2019-19307 — Critical (CVSS 9.8): An integer overflow in parse_mqtt in mongoose.c in Cesanta Mongoose 6.16 allows an attacker to achieve remote DoS…
CVE-2019-12951 — Critical (CVSS 9.8): An issue was discovered in Mongoose before 6.15. The parse_mqtt() function in mg_mqtt.c has a critical heap-based…
CVE-2018-20356 — Critical (CVSS 9.8): An invalid read of 8 bytes due to a use-after-free vulnerability in the mg_http_free_proto_data_cgi function call in…
CVE-2018-20355 — Critical (CVSS 9.8): An invalid write of 8 bytes due to a use-after-free vulnerability in the mg_http_free_proto_data_cgi function call in…

All CVEs affecting Cesanta Mongoose →

Other CWE-697 vulnerabilities

CVE-2026-75110 — Critical (CVSS 9.8): MemOS is a memory operating system for LLMs and AI agents. In deployments where authentication is enabled…
CVE-2025-54336 — Critical (CVSS 9.8): In Plesk Obsidian 18.0.70, _isAdminPasswordValid uses an == comparison. Thus, if the correct password is "0e" followed…
CVE-2024-24621 — Critical (CVSS 9.8): Softaculous Webuzo contains an authentication bypass vulnerability through the password reset functionality. Remote,…
CVE-2024-5217 — Critical (CVSS 9.8): ServiceNow has addressed an input validation vulnerability that was identified in the Washington DC, Vancouver, and…
CVE-2023-32571 — Critical (CVSS 9.8): Dynamic Linq 1.0.7.10 through 1.2.25 before 1.3.0 allows attackers to execute arbitrary code and commands when…
CVE-2022-47034 — Critical (CVSS 9.8): A type juggling vulnerability in the component /auth/fn.php of PlaySMS v1.4.5 and earlier allows attackers to bypass…

Browse all CWE-697 vulnerabilities →