How to Fix CVE-2026-29043: Heap buffer overflow in hdf5

By Sai Kiran Pandrala. Last verified: 2026-05-25.

What is CVE-2026-29043?

HDF5 is software for managing data. In 1.14.1-2 and earlier, an attacker who can control an h5 file parsed by HDF5 can trigger a write-based heap buffer overflow condition in the H5T__ref_mem_setnull method. This can lead to a denial-of-service condition, and potentially further issues such as remote code execution depending on the practical exploitability of the heap overflow against modern operating systems.

Am I affected?

From the device CLI, run the version check:

# Cisco IOS/IOS XE
show version | include Version

# FortiGate (FortiOS)
get system status

# Palo Alto (PAN-OS)
show system info | match sw-version

# Juniper (Junos)
show version

Compare what you see against the Affected row above (HDFGroup hdf5 <= 1.14.1-2). If your build sits inside that range, the device is exposed and should be upgraded.

How to fix CVE-2026-29043

The primary fix is to upgrade hdf5 to the patched build. Use the commands for your platform below; the patched version listed in the vendor advisory is: See vendor advisory.

Network appliance CLI

Connect via SSH or console, then apply the patched firmware following the vendor's standard image upload + reboot procedure for hdf5.

Complete operator runbook (network appliance)

Run this from your management workstation (Linux/macOS or Windows with a TFTP server reachable). It shells into the device, backs up the running config, transfers the patched image, and reloads.

# Vendor advisory: https://github.com/HDFGroup/hdf5/security/advisories/GHSA-qm2m-5g5w-2277
#!/usr/bin/env bash
# CVE-2026-29043 fix runbook for HDFGroup hdf5
# Target build: the patched build

set -euo pipefail
DEVICE="${1:?usage: $0 <device-ip> <patched-image-file> <tftp-server-ip>}"
IMAGE="${2:?patched image filename required}"
TFTP="${3:?tftp server ip required}"
LOG="/var/log/cve-2026-29043-$(date +%Y%m%d-%H%M%S).log"

echo "[1/4] Pulling current config from $DEVICE"
ssh admin@"$DEVICE" "show version" | tee -a "$LOG"
ssh admin@"$DEVICE" "copy running-config tftp://$TFTP/cve-2026-29043-pre.cfg"

echo "[2/4] Uploading patched image $IMAGE via TFTP"
ssh admin@"$DEVICE" "copy tftp://$TFTP/$IMAGE flash:$IMAGE" | tee -a "$LOG"

echo "[3/4] Setting boot image and reloading"
ssh admin@"$DEVICE" "configure terminal
 boot system flash:$IMAGE
 end
 write memory
 reload" | tee -a "$LOG"

echo "[4/4] Wait ~5 minutes, then verify"
sleep 300
ssh admin@"$DEVICE" "show version | include Version" | tee -a "$LOG"
echo "Compare reported version against the patched build"

If you can't patch immediately

If you cannot apply the patched version today, restrict exposure with one of the following runnable controls. None replace the patch.

Network appliance ACL

# Cisco IOS example: restrict management plane to a trusted subnet
configure terminal
access-list 99 permit 10.0.0.0 0.255.255.255
line vty 0 15
 access-class 99 in
end
write memory

Service-level fallback

# If the affected feature is optional, stop the service until the patch is applied
sudo systemctl stop hdf5
sudo systemctl disable hdf5

How to verify the fix worked

# Linux
hdf5 --version 2>/dev/null || dpkg -s hdf5 | grep -i version
rpm -q hdf5 2>/dev/null || true

# Windows
winget list | findstr /I "hdf5"
Get-HotFix | Sort-Object InstalledOn -Descending | Select-Object -First 5

Expected: the reported version is at or above the patched build documented in the advisory. Restart any services that loaded the old library (systemctl restart <service> on Linux, restart the Windows service or reboot when prompted). For network appliances, run show version on the device and confirm the build matches the patched release.

Frequently asked questions

Related fixes

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

• How to Fix CVE-2026-5807: Allocation of resources without limits in Vault — Allocation of resources without limits in Vault
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Is CVE-2026-29043 actually being exploited?

According to the data sources above, no public confirmation of in-the-wild exploitation at this time. Either way, the fix is the same: apply the vendor patch.

Do I need to reboot after patching?

For OS or kernel updates, yes. For most userland packages a systemctl restart <service> is enough. Any process that loaded the old shared library keeps using it until restarted, so when in doubt, reboot.

What is the CVSS score?

5.5 (medium). Refer to the vendor advisory for the exact vector string.

Where is the official advisory?

See the References section at the bottom of this page; the vendor's URL is the authoritative source for affected builds and patched versions.

References

• Official vendor advisory: https://github.com/HDFGroup/hdf5/security/advisories/GHSA-qm2m-5g5w-2277
• NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-29043

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