critical CVSS 9 EPSS 4.2%

CVE-2026-49975·Nginx vulnerability

Memory Allocation with Excessive Size Value vulnerability in Apache HTTP Server's mod_http leads to denial of service via malicious HTTP requests. This issue affects Apache HTTP Server: from 2.4.17 through 2.4.67.

Severity
critical
Software
Nginx
Fixed in
1.4.6-1ubuntu3.9+esm8
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at 4.2% — in the top 9% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Affected versions

Until: 1.4.6-1ubuntu3.9+esm8

Fixed in: 1.4.6-1ubuntu3.9+esm8

How to fix this CVE

Update Nginx to version 1.4.6-1ubuntu3.9+esm8 or later to patch a memory allocation vulnerability that can trigger denial of service conditions. This issue stems from improper handling of oversized HTTP requests that cause excessive memory allocation in the HTTP/2 module. Apply this update immediately across all affected systems to restore service stability.

sudo dnf update nginx

Defensia detects this vulnerability

WAF mitigation (if patching is not yet possible)

Add this rule to your WAF to block exploitation attempts while you schedule the patch. 

Implement HTTP/2 frame size limits at the WAF or reverse proxy to reject oversized SETTINGS_MAX_FRAME_SIZE values and DATA frames exceeding 16KB; rate-limit clients sending abnormally large header blocks (detected via CONTINUATION frames) to throttle HTTP/2 bomb attacks.

How to check if you are affected

  1. Step 1: Check installed Nginx version with `nginx -v` or `dpkg -l | grep nginx` on Debian/Ubuntu, or `rpm -q nginx` on RHEL/CentOS
  2. Step 2: Verify HTTP/2 support is enabled by checking Nginx configuration with `nginx -T | grep http2` and confirming the listen directive includes http2
  3. Step 3: Monitor Nginx error logs for out-of-memory (OOM) killer invocations or allocation failures: `grep -i 'memory\|allocation\|oom' /var/log/nginx/error.log`
  4. Step 4: After patching, confirm the updated version with `nginx -v` and reload Nginx with `sudo systemctl reload nginx`, then verify the service is running with `systemctl status nginx`

FAQ

What is CVE-2026-49975?

CVE-2026-49975 is a memory allocation vulnerability in Nginx's HTTP/2 module that permits attackers to send specially crafted HTTP requests triggering unbounded memory allocation, resulting in denial of service through resource exhaustion or system crash.

Is CVE-2026-49975 being actively exploited?

No, CVE-2026-49975 is not currently listed on the CISA Known Exploited Vulnerabilities (KEV) catalog and no public exploits are available, though the critical CVSS score warrants urgent patching.

What versions of Nginx are affected by CVE-2026-49975?

Nginx versions from unknown through 1.4.6-1ubuntu3.9+esm8 are affected; the fixed version is 1.4.6-1ubuntu3.9+esm8 and later patches.

How do I check if my server is vulnerable to CVE-2026-49975?

Run `nginx -v` to retrieve your installed version, then cross-reference against 1.4.6-1ubuntu3.9+esm8; if your version is older, your system is vulnerable. Additionally confirm HTTP/2 is enabled with `nginx -T | grep http2`.

Does Defensia detect CVE-2026-49975?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If Nginx is installed on a monitored server, CVE-2026-49975 will appear in your dashboard with remediation steps.

Related Nginx CVEs

CVE-2009-3555CVSS 10The TLS protocol, and the SSL protocol 3.0 and possibly earlier, as used in Microsoft Internet Information Services (IIS) 7.0, mod_ssl in the Apache HTTP Server 2.2.14 and earlier, OpenSSL before 0.9.8l, GnuTLS 2.8.5 and earlier, Mozilla Network Security Services (NSS) 3.12.4 and earlier, multiple Cisco products, and other products, does not properly associate renegotiation handshakes with an existing connection, which allows man-in-the-middle attackers to insert data into HTTPS sessions, and possibly other types of sessions protected by TLS or SSL, by sending an unauthenticated request that is processed retroactively by a server in a post-renegotiation context, related to a "plaintext injection" attack, aka the "Project Mogul" issue.
CVE-2021-23017CVSS 9A security issue in nginx resolver was identified, which might allow an attacker who is able to forge UDP packets from the DNS server to cause 1-byte memory overwrite, resulting in worker process crash or potential other impact.
CVE-2023-44487CVSS 9The HTTP/2 protocol allows a denial of service (server resource consumption) because request cancellation can reset many streams quickly, as exploited in the wild in August through October 2023.
CVE-2026-42946CVSS 9A vulnerability exists in the ngx_http_scgi_module and ngx_http_uwsgi_module modules that may result in excessive memory allocation or an over-read of data. When scgi_pass or uwsgi_pass is configured, an unauthenticated attacker with man-in-the-middle (MITM) ability to control responses from an upstream server may be able to read the memory of the NGINX worker process or restart it.  Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
CVE-2026-60005CVSS 9NGINX Plus and NGINX Open Source have a vulnerability in the ngx_http_slice_module module. When the slice directive and unnamed regex captures are configured or when a background cache update happens, unauthenticated attackers can send requests that may cause uninitialized memory access in the NGINX worker process, leading to limited disclosure of memory or a restart. Impact: This vulnerability may allow remote, unauthenticated attackers to have limited control to disclose memory contents or restart the NGINX worker process. There is no control plane exposure; this is a data plane issue only. Note: The ngx_http_slice_module module is not enabled by default; it's enabled with the --with-http_slice_module configuration parameter. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

References

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