Skip to content
Noroxi
NVD / CVE Program· CNA apache

CVE-2021-41524: null pointer dereference in h2 fuzzing

Noroxi assessment

Priority: Monitor (action score 38/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 25.1% (FIRST EPSS); higher than 97.9% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: apache2 (Alpine:v3.11) 2.4.50-r0; apache2 (Debian:12) 2.4.50-1; jbcs-httpd24-httpd (Red Hat:jboss_core_services:1::el7) 0:2.4.51-28.el7jbcs.

Low priority for now. Upgrade to apache2 (Alpine:v3.11) 2.4.50-r0; apache2 (Debian:12) 2.4.50-1; jbcs-httpd24-httpd (Red Hat:jboss_core_services:1::el7) 0:2.4.51-28.el7jbcs or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

While fuzzing the 2.4.49 httpd, a new null pointer dereference was detected during HTTP/2 request processing, allowing an external source to DoS the server. This requires a specially crafted request. The vulnerability was recently introduced in version 2.4.49. No exploit is known to the project.

HighCVSS 7.5 · v3.1—No exploit Fix available
Published
Oct 5, 2021
Updated
Jun 17, 2026
EPSS
25.1% · 97th percentile

Report tools

JSON

Action score

38

Monitor

Low priority for now.

CVSS
30 / 40 · 7.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
8 / 30 · 25.1%

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2021-41524

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

One daily email digest (06:00 UTC); connect a webhook for KEV listings and weaponized exploits instantly.

Your free account also gets you

Running WordPress? Scan your site free with WP Lens

  • Stack alerts: add the products and versions you run, get the new CVEs that affect them
  • Uptime monitoring: 1 site, instant email when it goes down
  • Add your domain: subdomains and takeover risk scanned every week (1 domain)
  • 10 scans an hour on the security tools (3 a day without an account), an API key and MCP
  • All your scans in one panel: findings, what changed in the last scan, a report per domain or per client (PDF, share link)
All free tools

Sign up with email · Have an account? Sign in

Free account, no card. Unfollow any time.

Don't want an account? Get "Exploited this week" by email every MondayDon't want an account? RSS feed for apache records

Running WordPress? Scan your site free with WP Lens

Is your version affected? Check it

Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

We use this product, ask for help

Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
apachehttp server
fedoraprojectfedora
oracleinstantis enterprisetrack
netappcloud backup

Using http server? Add it to your stack and be the first to know about CVEs like this one. (Apache HTTP)

Watch new CVEs for http server

When you'll hear from us

  • when a new CVE affecting this product is published
  • when a record in your stack enters KEV or gets exploit code

One daily email digest (06:00 UTC); connect a webhook for KEV listings and weaponized exploits instantly.

Your free account also gets you

Running WordPress? Scan your site free with WP Lens

  • Stack alerts: add the products and versions you run, get the new CVEs that affect them
  • Uptime monitoring: 1 site, instant email when it goes down
  • Add your domain: subdomains and takeover risk scanned every week (1 domain)
  • 10 scans an hour on the security tools (3 a day without an account), an API key and MCP
  • All your scans in one panel: findings, what changed in the last scan, a report per domain or per client (PDF, share link)
All free tools

Sign up with email · Have an account? Sign in

Free account, no card. Unfollow any time.

Don't want an account? Get "Exploited this week" by email every Monday

Is Apache HTTP Server on your server exposed to the internet?

The free port scanner finds the open ports on your server and matches the service versions it can read against known vulnerabilities. No account needed.

Run a port scan

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • apache http server2.4.49

Versions reported by the vendor

Affected version ranges reported by the assigning authority (apache). Independent of NVD's CPE analysis and usually ahead of it.

  • Apache Software Foundation Apache HTTP Server

    • 2.4.49affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Alpine:v3.11apache2before 2.4.50-r02.4.50-r0
Debian:12apache2before 2.4.50-12.4.50-1
Red Hat:jboss_core_services:1::el7jbcs-httpd24-httpdbefore 0:2.4.51-28.el7jbcs0:2.4.51-28.el7jbcs
Red Hat:jboss_core_services:1::el7jbcs-httpd24-httpd-debuginfobefore 0:2.4.51-28.el7jbcs0:2.4.51-28.el7jbcs
Red Hat:jboss_core_services:1::el7jbcs-httpd24-httpd-develbefore 0:2.4.51-28.el7jbcs0:2.4.51-28.el7jbcs
Red Hat:jboss_core_services:1::el7jbcs-httpd24-httpd-manualbefore 0:2.4.51-28.el7jbcs0:2.4.51-28.el7jbcs
Red Hat:jboss_core_services:1::el7jbcs-httpd24-httpd-selinuxbefore 0:2.4.51-28.el7jbcs0:2.4.51-28.el7jbcs
Red Hat:jboss_core_services:1::el7jbcs-httpd24-httpd-toolsbefore 0:2.4.51-28.el7jbcs0:2.4.51-28.el7jbcs
Red Hat:jboss_core_services:1::el7jbcs-httpd24-mod_ldapbefore 0:2.4.51-28.el7jbcs0:2.4.51-28.el7jbcs
Red Hat:jboss_core_services:1::el7jbcs-httpd24-mod_proxy_htmlbefore 1:2.4.51-28.el7jbcs1:2.4.51-28.el7jbcs
Red Hat:jboss_core_services:1::el7jbcs-httpd24-mod_sessionbefore 0:2.4.51-28.el7jbcs0:2.4.51-28.el7jbcs
Red Hat:jboss_core_services:1::el7jbcs-httpd24-mod_sslbefore 1:2.4.51-28.el7jbcs1:2.4.51-28.el7jbcs
Red Hat:jboss_core_services:1::el8jbcs-httpd24-httpdbefore 0:2.4.51-28.el8jbcs0:2.4.51-28.el8jbcs
Red Hat:jboss_core_services:1::el8jbcs-httpd24-httpd-debuginfobefore 0:2.4.51-28.el8jbcs0:2.4.51-28.el8jbcs
Red Hat:jboss_core_services:1::el8jbcs-httpd24-httpd-develbefore 0:2.4.51-28.el8jbcs0:2.4.51-28.el8jbcs
Red Hat:jboss_core_services:1::el8jbcs-httpd24-httpd-manualbefore 0:2.4.51-28.el8jbcs0:2.4.51-28.el8jbcs
Red Hat:jboss_core_services:1::el8jbcs-httpd24-httpd-selinuxbefore 0:2.4.51-28.el8jbcs0:2.4.51-28.el8jbcs
Red Hat:jboss_core_services:1::el8jbcs-httpd24-httpd-toolsbefore 0:2.4.51-28.el8jbcs0:2.4.51-28.el8jbcs
Red Hat:jboss_core_services:1::el8jbcs-httpd24-httpd-tools-debuginfobefore 0:2.4.51-28.el8jbcs0:2.4.51-28.el8jbcs
Red Hat:jboss_core_services:1::el8jbcs-httpd24-mod_ldapbefore 0:2.4.51-28.el8jbcs0:2.4.51-28.el8jbcs
Red Hat:jboss_core_services:1::el8jbcs-httpd24-mod_ldap-debuginfobefore 0:2.4.51-28.el8jbcs0:2.4.51-28.el8jbcs
Red Hat:jboss_core_services:1::el8jbcs-httpd24-mod_proxy_htmlbefore 1:2.4.51-28.el8jbcs1:2.4.51-28.el8jbcs
Red Hat:jboss_core_services:1::el8jbcs-httpd24-mod_proxy_html-debuginfobefore 1:2.4.51-28.el8jbcs1:2.4.51-28.el8jbcs
Red Hat:jboss_core_services:1::el8jbcs-httpd24-mod_sessionbefore 0:2.4.51-28.el8jbcs0:2.4.51-28.el8jbcs

+3

Same product

apache: all records

Other highest-scoring records for the same primary product.

  • CVE-2021-42013Path Traversal and Remote Code Execution in Apache HTTP Server 2.4.49 and 2.4.50 (incomplete fix of CVE-2021-41773)KEV
    99Now
  • CVE-2021-41773Path traversal and file disclosure vulnerability in Apache HTTP Server 2.4.49KEV
    99Now
  • CVE-2024-38475Apache HTTP Server weakness in mod_rewrite when first segment of substitution matches filesystem path.KEV
    96Now

Published before and after this one in the same product

  • ← EarlierCVE-2021-36160Sep 16, 2021 · mod_proxy_uwsgi out of bound read
    49Plan
  • ← EarlierCVE-2021-39275Sep 16, 2021 · ap_escape_quotes buffer overflow
    51Plan
  • Later →CVE-2021-44224Dec 20, 2021 · Possible NULL dereference or SSRF in forward proxy configurations in Apache HTTP Server 2.4.51 and earlier
    57Plan

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
alpine:apache22.4.50-r0 · Alpine:v3.11Package registry (OSV)
debian:apache22.4.50-1 · Debian:12Package registry (OSV)
red hat:jbcs-httpd24-httpd0:2.4.51-28.el7jbcs · Red Hat:jboss_core_services:1::el7Package registry (OSV)
red hat:jbcs-httpd24-httpd-debuginfo0:2.4.51-28.el7jbcs · Red Hat:jboss_core_services:1::el7Package registry (OSV)
red hat:jbcs-httpd24-httpd-devel0:2.4.51-28.el7jbcs · Red Hat:jboss_core_services:1::el7Package registry (OSV)
red hat:jbcs-httpd24-httpd-manual0:2.4.51-28.el7jbcs · Red Hat:jboss_core_services:1::el7Package registry (OSV)
red hat:jbcs-httpd24-httpd-selinux0:2.4.51-28.el7jbcs · Red Hat:jboss_core_services:1::el7Package registry (OSV)
red hat:jbcs-httpd24-httpd-tools0:2.4.51-28.el7jbcs · Red Hat:jboss_core_services:1::el7Package registry (OSV)
red hat:jbcs-httpd24-httpd-tools-debuginfo0:2.4.51-28.el8jbcs · Red Hat:jboss_core_services:1::el8Package registry (OSV)
red hat:jbcs-httpd24-mod_ldap0:2.4.51-28.el7jbcs · Red Hat:jboss_core_services:1::el7Package registry (OSV)
red hat:jbcs-httpd24-mod_ldap-debuginfo0:2.4.51-28.el8jbcs · Red Hat:jboss_core_services:1::el8Package registry (OSV)
red hat:jbcs-httpd24-mod_proxy_html1:2.4.51-28.el7jbcs · Red Hat:jboss_core_services:1::el7Package registry (OSV)
red hat:jbcs-httpd24-mod_session0:2.4.51-28.el7jbcs · Red Hat:jboss_core_services:1::el7Package registry (OSV)
red hat:jbcs-httpd24-mod_ssl1:2.4.51-28.el7jbcs · Red Hat:jboss_core_services:1::el7Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-476 · NULL Pointer Dereference

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (7 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records