⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● Medium · CVSS 6.5

How to Fix CVE-2026-5265: Improper Handling of Length Parameter Inconsistency

By Sai Kiran Pandrala

Other vulnerabilities in the same area that are worth patching alongside this one:

Last verified: 2026-05-25

CVE-2026-5265 is a improper handling of length parameter inconsistency in Red Hat Fast Datapath for Red Hat Enterprise Linux 8. Fix it by upgrading to 0:21.12.0-145.el8fdp, 0:23.06.4-30.el8fdp, 0:23.06.4-30.el9fdp, 0:23.09.6-16.el9fdp, 0:24.03.7-82.el9fdp, 0:25.03.2-100.el9fdp.

⚡ At a glance
SeverityCVSS 6.5 - Medium
Actively exploited?Not currently in the CISA KEV catalog
AffectedSee vendor advisory for affected versions
Fixed in0:21.12.0-145.el8fdp, 0:23.06.4-30.el8fdp, 0:23.06.4-30.el9fdp, 0:23.09.6-16.el9fdp, 0:24.03.7-82.el9fdp, 0:25.03.2-100.el9fdp
Type (CWE)CWE-130: Improper Handling of Length Parameter Inconsistency

What is CVE-2026-5265?

CVE-2026-5265 is a improper handling of length parameter inconsistency flaw in Red Hat Fast Datapath for Red Hat Enterprise Linux 8. It carries a CVSS base score of 6.5 (medium). It is not currently listed in the CISA Known Exploited Vulnerabilities catalog.

From the source record: When generating an ICMP Destination Unreachable or Packet Too Big response, the handler copies a portion of the original packet into the ICMP error body using the IP header's self-declared total length (ip_tot_len for IPv4, ip6_plen for IPv6) without validating it against the actual packet buffer size. A VM can send a short packet with an inflated IP length field that triggers an ICMP error (e.g., by hitting a reject ACL), causing ovn-controller to read heap memory beyond the valid packet data and include it in the ICMP response sent back to the VM.

Why it matters in practice: The blast radius depends on how the affected service is exposed. An internet-facing instance with no compensating controls is the highest-risk configuration.

Am I affected?

You are affected if your installation of Fast Datapath for Red Hat Enterprise Linux 8 matches a version listed in the Affected row above.


# Debian/Ubuntu
dpkg -s fast | grep Version
# RHEL/Rocky
rpm -q fast

How to fix CVE-2026-5265

Apply the vendor patch. Target the build named in the Fixed in row above (0:21.12.0-145.el8fdp, 0:23.06.4-30.el8fdp, 0:23.06.4-30.el9fdp, 0:23.09.6-16.el9fdp, 0:24.03.7-82.el9fdp, 0:25.03.2-100.el9fdp). The runnable command set below covers the most common deployment patterns for Fast Datapath for Red Hat Enterprise Linux 8.

Ubuntu / Debian


sudo apt-get update
sudo apt-get install --only-upgrade fast
dpkg -s fast | grep Version

RHEL / CentOS / Rocky


sudo dnf upgrade fast -y
rpm -q fast

After applying the patch

  1. Restart the service or device so the patched binary loads.
  2. Confirm the running version matches the Fixed in row using the verification command below.
  3. Rotate credentials and API keys that the affected service could access if the asset was exposed during the disclosure window.

If you can't patch immediately

Until the patch lands, narrow the attack surface with these runnable controls.

Restrict network exposure

Block public access to the affected service at the perimeter. Allow only trusted source IPs.


# Linux iptables: only allow trusted admin subnet
sudo iptables -A INPUT -p tcp --dport 443 -s 10.10.10.0/24 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 443 -j DROP
sudo iptables-save | sudo tee /etc/iptables/rules.v4


# Windows firewall: only allow trusted admin subnet on management port
New-NetFirewallRule -DisplayName "Restrict-Mgmt-Allow" -Direction Inbound -Action Allow `
  -RemoteAddress 10.10.10.0/24 -Protocol TCP -LocalPort 443
New-NetFirewallRule -DisplayName "Restrict-Mgmt-Deny"  -Direction Inbound -Action Block `
  -Protocol TCP -LocalPort 443

Mitigations are temporary. Apply the vendor patch as soon as a maintenance window opens.

How to verify the fix worked

Confirm the patched build is the one actually running.


# Debian/Ubuntu
dpkg -s fast | grep Version
# RHEL/Rocky
rpm -q fast

Expected: a version at or above 0:21.12.0-145.el8fdp, 0:23.06.4-30.el8fdp, 0:23.06.4-30.el9fdp, 0:23.09.6-16.el9fdp, 0:24.03.7-82.el9fdp, 0:25.03.2-100.el9fdp.

Also worth doing: pull recent log windows for indicators of compromise listed in the vendor advisory, and re-run an authenticated vulnerability scan with up-to-date signatures.

Frequently asked questions

Is CVE-2026-5265 being exploited in the wild?

As of 2026-05-25, CVE-2026-5265 is not listed in the CISA Known Exploited Vulnerabilities catalog. Watch the catalog and patch on a normal cadence; KEV status can change as exploitation evidence emerges.

What is the CVSS score for CVE-2026-5265?

The CVSS base score is 6.5 (Medium).

What version fixes this?

Upgrade to 0:21.12.0-145.el8fdp, 0:23.06.4-30.el8fdp, 0:23.06.4-30.el9fdp, 0:23.09.6-16.el9fdp, 0:24.03.7-82.el9fdp, 0:25.03.2-100.el9fdp.

Will a WAF or IDS rule alone close this?

No. Network filters cut down opportunistic scans but they do not remove the flaw. The vendor patch is the only durable fix.

References

*Assembled from the official vendor advisory, the NVD record, and the CISA KEV listing on 2026-05-25. Always confirm against the vendor advisory before applying changes in production.*