CVE-2021-26691

highpriority · attend · 63EPSS 0.683 · 99 %ileDEEURUUS
grimoire priorityP1 · Urgent
Exploitable?
—
no known exploitation
Likely / severe?
68.3% (99th) EPSS
CVSS 7.5 · high
Is it mine?
81 products
Check your exposure
Who says so?
6 sources
cnnvd · enisa_euvd · fstec_bdu · cert_bund

EPSS · scored 2026-10-24

In Apache HTTP Server versions 2.4.0 to 2.4.46 a specially crafted SessionHeader sent by an origin server could cause a heap overflow

01

remediations

Vendor fix, mitigation, or workaround guidance, as published by each source.

No vendor fix yet; a mitigation is available.

  • MitigationMELSOFT iQ AppPortal (SW1DND-IQAPL-M)cisa_csaf_ot

    Install an antivirus software in the personal computer that runs this product.

02

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⚠ sources disagree · high–critical · 7.5–9.8

v2.07.5highAV:N/AC:L/Au:N/C:P/I:P/A:Pprimary · NVD / NIST USexploitability 10 · impact 6.4
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
v3.09.8criticalCVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsecondary · CISA US
v3.19.8criticalAV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsecondary · FSTEC (BDU) RU
v3.19.8criticalCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:Hsecondary · CVSS-BT (t0sche)
03

weaknesses

The CWE weakness classes this flaw belongs to.

CWE-787USprimaryCWE-122USCWE-122USCWE-787USCWE-787US
04

affected products (81)

Products and version ranges known to be affected.

showing 20 of 81
05

advisories (5)

Vendor and ecosystem advisories describing this.

  • WID-SEC-W-2022-0438Apache HTTP Server: Mehrere SchwachstellenDeutsch2021-06-09csaf · cert_bundDE

    Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in Apache HTTP Server ausnutzen, um einen Denial of Service Angriff durchzuführen, Sicherheitsvorkehrungen zu umgehen oder sonstige Auswirkungen zu verursachen.

  • WID-SEC-W-2024-0064Juniper Produkte: Mehrere SchwachstellenDeutsch2024-01-10csaf · cert_bundDE

    Ein Angreifer aus dem angrenzenden Netzwerk oder ein entfernter, anonymer, authentisierter, lokaler oder physischer Angreifer kann mehrere Schwachstellen in Juniper JUNOS, Juniper JUNOS Evolved, Juniper SRX Series, Juniper EX Series, Juniper QFX Series, Juniper ACX Series, Juniper PTX Series und Juniper MX Series ausnutzen, um beliebigen Code auszuführen, Sicherheitsmaßnahmen zu umgehen, vertrauliche Informationen offenzulegen, einen Denial-of-Service-Zustand herbeizuführen und seine Berechtigungen zu erweitern.

  • WID-SEC-W-2024-1591Juniper JUNOS: Mehrere SchwachstellenDeutsch2024-07-10csaf · cert_bundDE

    Ein Angreifer kann mehrere Schwachstellen in Juniper JUNOS ausnutzen, um einen Denial of Service zu verursachen, Informationen offenzulegen, Privilegien zu erweitern und Sicherheitsmechanismen inklusive zu umgehen.

  • ICSA-22-132-02Mitsubishi Electric MELSOFT iQ AppPortal2022-05-12icsa · cisa_csaf_otUS

    Successful exploitation of these vulnerabilities could result in a denial-of-service condition, malicious program execution, information disclosure, information tampering, or authentication bypass.

  • BIT-apache-2021-26691Apache HTTP Server mod_session response handling heap overflow2024-03-06vendor · osvUS

    In Apache HTTP Server versions 2.4.0 to 2.4.46 a specially crafted SessionHeader sent by an origin server could cause a heap overflow

06

also known as (4)

Other names and identifiers for this entity.

07

sources

Which sources assert this record, and when.

cnnvdenisa_euvdfstec_bducert_bundcisa_csaf_otosvNVDCVE.orgMITRE
published 2021-06-10modified 2026-06-17
09

references (70)

External citations — patches, advisories, analysis.

scry

Attackers weaponise vulnerabilities like this against internet-exposed services. See what is exposed on your perimeter with a free passive scan.

Free scan