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NVD / CVE Program· CNA certcc

CVE-2016-1546: The Apache HTTP Server 2.4.17 and 2.4.18, when mod_http2 is enabled, does not limit the number of simultaneous stream workers for a single…

MediumCVSS 5.9 · v3.0—No exploit Fix available

Noroxi assessment

Priority: Monitor (action score 28/100)

  • 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: 15.9% (FIRST EPSS); higher than 96.9% 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. Special conditions such as timing or configuration are required.
  • Fixed version: apache2 (Debian:12) 2.4.20-1; httpd24-httpd (Red Hat:rhel_software_collections:2::el6) 0:2.4.25-9.el6; httpd24-httpd-debuginfo (Red Hat:rhel_software_collections:2::el6) 0:2.4.25-9.el6.

Low priority for now. Upgrade to apache2 (Debian:12) 2.4.20-1; httpd24-httpd (Red Hat:rhel_software_collections:2::el6) 0:2.4.25-9.el6; httpd24-httpd-debuginfo (Red Hat:rhel_software_collections:2::el6) 0:2.4.25-9.el6 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

The Apache HTTP Server 2.4.17 and 2.4.18, when mod_http2 is enabled, does not limit the number of simultaneous stream workers for a single HTTP/2 connection, which allows remote attackers to cause a denial of service (stream-processing outage) via modified flow-control windows.

Published
Jul 6, 2016
Updated
Jun 16, 2026
EPSS
15.9% · 96th percentile

Report tools

JSON

Action score

28

Monitor

Low priority for now.

CVSS
23 / 40 · 5.9 / 10
CISA KEV
0 / 30 · Not listed
EPSS
5 / 30 · 15.9%

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.

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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

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Noroxi analysis

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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

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When you'll hear from us

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

One daily email digest (06:00 UTC); connect a webhook for KEV listings and weaponized exploits every 10 minutes on paid plans, on the hour on the free plan.

Is Apache HTTP Server on your server exposed to the internet?Run a port scan

Your free account also gets you

  • CVE 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, at most 30 a day (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

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Affected versions

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

  • apache http server2.4.17
  • apache http server2.4.18

Package-level exposure

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

EcosystemPackageAffected rangeFix
Debian:12apache2before 2.4.20-12.4.20-1
Red Hat:rhel_software_collections:2::el6httpd24-httpdbefore 0:2.4.25-9.el60:2.4.25-9.el6
Red Hat:rhel_software_collections:2::el6httpd24-httpd-debuginfobefore 0:2.4.25-9.el60:2.4.25-9.el6
Red Hat:rhel_software_collections:2::el6httpd24-httpd-develbefore 0:2.4.25-9.el60:2.4.25-9.el6
Red Hat:rhel_software_collections:2::el6httpd24-httpd-manualbefore 0:2.4.25-9.el60:2.4.25-9.el6
Red Hat:rhel_software_collections:2::el6httpd24-httpd-toolsbefore 0:2.4.25-9.el60:2.4.25-9.el6
Red Hat:rhel_software_collections:2::el6httpd24-mod_ldapbefore 0:2.4.25-9.el60:2.4.25-9.el6
Red Hat:rhel_software_collections:2::el6httpd24-mod_proxy_htmlbefore 1:2.4.25-9.el61:2.4.25-9.el6
Red Hat:rhel_software_collections:2::el6httpd24-mod_sessionbefore 0:2.4.25-9.el60:2.4.25-9.el6
Red Hat:rhel_software_collections:2::el6httpd24-mod_sslbefore 1:2.4.25-9.el61:2.4.25-9.el6
Red Hat:rhel_software_collections:2::el7httpd24-httpdbefore 0:2.4.25-9.el70:2.4.25-9.el7
Red Hat:rhel_software_collections:2::el7httpd24-httpd-debuginfobefore 0:2.4.25-9.el70:2.4.25-9.el7
Red Hat:rhel_software_collections:2::el7httpd24-httpd-develbefore 0:2.4.25-9.el70:2.4.25-9.el7
Red Hat:rhel_software_collections:2::el7httpd24-httpd-manualbefore 0:2.4.25-9.el70:2.4.25-9.el7
Red Hat:rhel_software_collections:2::el7httpd24-httpd-toolsbefore 0:2.4.25-9.el70:2.4.25-9.el7
Red Hat:rhel_software_collections:2::el7httpd24-mod_ldapbefore 0:2.4.25-9.el70:2.4.25-9.el7
Red Hat:rhel_software_collections:2::el7httpd24-mod_proxy_htmlbefore 1:2.4.25-9.el71:2.4.25-9.el7
Red Hat:rhel_software_collections:2::el7httpd24-mod_sessionbefore 0:2.4.25-9.el70:2.4.25-9.el7
Red Hat:rhel_software_collections:2::el7httpd24-mod_sslbefore 1:2.4.25-9.el71:2.4.25-9.el7

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-2015-3183Jul 20, 2015 · The chunked transfer coding implementation in the Apache HTTP Server before 2.4.14 does not properly parse chunk headers, which allows…
    42Plan
  • ← EarlierCVE-2015-3185Jul 20, 2015 · The ap_some_auth_required function in server/request.c in the Apache HTTP Server 2.4.x before 2.4.14 does not consider that a Require…
    22Monitor
  • Later →CVE-2016-4979Jul 6, 2016 · The Apache HTTP Server 2.4.18 through 2.4.20, when mod_http2 and mod_ssl are enabled, does not properly recognize the "SSLVerifyClient…
    36Monitor

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
debian:apache22.4.20-1 · Debian:12Package registry (OSV)
red hat:httpd24-httpd0:2.4.25-9.el6 · Red Hat:rhel_software_collections:2::el6Package registry (OSV)
red hat:httpd24-httpd-debuginfo0:2.4.25-9.el6 · Red Hat:rhel_software_collections:2::el6Package registry (OSV)
red hat:httpd24-httpd-devel0:2.4.25-9.el6 · Red Hat:rhel_software_collections:2::el6Package registry (OSV)
red hat:httpd24-httpd-manual0:2.4.25-9.el6 · Red Hat:rhel_software_collections:2::el6Package registry (OSV)
red hat:httpd24-httpd-tools0:2.4.25-9.el6 · Red Hat:rhel_software_collections:2::el6Package registry (OSV)
red hat:httpd24-mod_ldap0:2.4.25-9.el6 · Red Hat:rhel_software_collections:2::el6Package registry (OSV)
red hat:httpd24-mod_proxy_html1:2.4.25-9.el6 · Red Hat:rhel_software_collections:2::el6Package registry (OSV)
red hat:httpd24-mod_session0:2.4.25-9.el6 · Red Hat:rhel_software_collections:2::el6Package registry (OSV)
red hat:httpd24-mod_ssl1:2.4.25-9.el6 · Red Hat:rhel_software_collections:2::el6Package 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.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Not on record for this CVE: patch commit or PR link · researcher credit · variant or chain candidate · public bounty program.

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.
  • Special conditions such as timing or configuration are required.

If successful

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

Weakness class (CWE)

CWE-399 · Resource Management Errors

CVSS vector

CVSS:3.0/AV:N/AC:H/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.

References

Show all references (19 more)

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

All records