CVE-2021-42756

criticalpriority · attend · 61EPSS 0.350 · 98 %ileexploit · PoCDEEURUUS

grimoire priorityP1 · Urgent

Exploitable?

Public exploit

1 exploit · PoC

Likely / severe?

35.0% (98th) EPSS

CVSS 9.8 · critical

Is it mine?

23 products

Check your exposure

Who says so?

5 sources

cnnvd · enisa_euvd · fstec_bdu · nvd

EPSS · scored 2026-10-27

Multiple stack-based buffer overflow vulnerabilities [CWE-121] in the proxy daemon of FortiWeb 5.x all versions, 6.0.7 and below, 6.1.2 and below, 6.2.6 and below, 6.3.16 and below, 6.4 all versions may allow an unauthenticated remote attacker to achieve arbitrary code execution via specifically crafted HTTP requests.

cvss

Technical severity, 0–10. One row per scoring source.

9.8

010

base score 0–10 · higher = more severe · hover a vector to decode

v3.19.8criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hprimary · NVD / NIST USexploitability 3.9 · impact 5.9

v3.19.8criticalAV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsecondary · FSTEC (BDU) RU

v3.19.3criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:P/RL:U/RC:Csecondary · ENISA EU

v3.19.8criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsecondary · psirt@fortinet.comexploitability 3.9 · impact 5.9

v3.19.3criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:Psecondary · CVSS-BT (t0sche)

ssvc

A stakeholder decision — act, attend, or track — from exploitation and impact.

Exploitation: none · Automatable: yes · Technical Impact: totalcoordinatorcisa_ssvcUS

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-787USprimaryCWE-121USCWE-121US

exploits (1)

Public proof-of-concept and weaponised exploit code.

3ndorph1n/CVE-2021-427563ndorph1n/CVE-2021-42756PoC · poc_in_github

affected products (23)

Products and version ranges known to be affected.

Fortinet FortiWeb≤ 5.7.0 ≤5.7.3enisa_euvdEU
Fortinet FortiWeb≤ 5.8.5 ≤5.8.7enisa_euvdEU
Fortinet FortiWeb≤ 6.1.0 ≤6.1.2enisa_euvdEU
Fortinet FortiWeb≤ 6.3.0 ≤6.3.16enisa_euvdEU
Fortinet FortiWeb≤ 5.9.0 ≤5.9.1enisa_euvdEU
Fortinet FortiWeb≤ 5.6.0 ≤5.6.2enisa_euvdEU
Fortinet FortiWeb≤ 6.2.0 ≤6.2.6enisa_euvdEU
Fortinet FortiWeb≤ 5.8.0 ≤5.8.3enisa_euvdEU
Fortinet FortiWeb≤ 6.4.0 ≤6.4.1enisa_euvdEU
Fortinet FortiWeb≤ 6.0.0 ≤6.0.7enisa_euvdEU
Fortinet FortiWeb5.6.0 → 5.6.*enisa_euvdEU
Fortinet FortiWeb5.7.0 → 5.7.*enisa_euvdEU
Fortinet FortiWeb5.8.0 → 5.8.*enisa_euvdEU
Fortinet Inc. FortiWeb5.6.0 → 6.0.8fstec_bduRU
Fortinet Inc. FortiWeb6.1.0 → 6.1.3fstec_bduRU
Fortinet Inc. FortiWeb6.2.0 → 6.2.7fstec_bduRU
Fortinet Inc. FortiWeb6.3.0 → 6.3.17fstec_bduRU
Fortinet Inc. FortiWeb6.4.0 → 6.4.2fstec_bduRU
fortinet fortiweb5.6.0 → 6.0.8nvdUScpe:2.3:a:fortinet:fortiweb:*:*:*:*:*:*:*:*
fortinet fortiweb6.1.0 → 6.1.3nvdUScpe:2.3:a:fortinet:fortiweb:*:*:*:*:*:*:*:*

showing 20 of 23

advisories (1)

Vendor and ecosystem advisories describing this.

WID-SEC-W-2023-0439Fortinet FortiWeb: Schwachstelle ermöglicht CodeausführungDeutsch2023-02-20csaf · cert_bundDE
Ein entfernter, anonymer Angreifer kann eine Schwachstelle in Fortinet FortiWeb ausnutzen, um beliebigen Programmcode auszuführen.

also known as (5)

Other names and identifiers for this entity.

sources

Which sources assert this record, and when.

cnnvd enisa_euvd fstec_bdu nvd cert_bund NVD CVE.org MITRE

published 2023-02-16modified 2026-06-17

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+16123 more

references (5)

External citations — patches, advisories, analysis.

scry

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