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BusyBox httpd: Authentication bypass for pre-compressed .gz files

CVE-2026-124738Medium 5.3

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Summary

When BusyBox httpd is built with pre-compressed file support (gzip content encoding), password rules are checked only against the requested path, not the .gz file actually served. A remote attacker can request the uncompressed path with Accept-Encoding: gzip to bypass protection on the compressed file and read sensitive content. Only confidentiality is affected, and exploitation requires password rules set on individual .gz files and network access to the service.

Affected

  • BusyBox httpd builds with the gzip (pre-compressed file) option enabled; affected versions: Unknown.
  • Red Hat Hardened Images: affected (per Red Hat CVE record).
  • Red Hat Enterprise Linux 6: unaffected by default (per Red Hat CVE record).
  • Red Hat Enterprise Linux (other versions): Unknown, sources conflict.

Fixed in

Unknown. No fixed version, errata or upstream BusyBox fix has been identified in the sources.

Workaround

  • Define authentication rules for the containing directory instead of individual file paths.
  • If file-level rules are required, protect both the base file and the .gz file (for example /secret.txt and /secret.txt.gz).
  • Restrict network access to the httpd service with local firewall rules if remote access is not required.
  • If pre-compressed serving is not needed, rebuild or reconfigure BusyBox without the gzip option.
  • Note: changing httpd.conf requires restarting or reloading httpd, which interrupts active sessions.

Exploitation

  • No evidence of exploitation in the wild.
  • Not listed in CISA KEV according to the sources.
  • No public proof of concept or exploit code indexed.
  • VulDB gives a speculative exploit price range of USD 5k to 25k; this is an estimate, not evidence of use.

Our recommendation

  • Identify whether any device, appliance or container runs BusyBox httpd with password-protected paths.
  • Check Red Hat Hardened Images in your environment, as Red Hat lists them as affected.
  • Apply the directory-level authentication or file-pair protection workaround now.
  • Restrict network exposure of httpd and disable the gzip option if it is not needed.
  • Track the vendor advisory and apply a fixed build once available.
  • Also review CVE-2026-124739 (rated 7.5) if BusyBox httpd is in use, as it is a more severe httpd flaw from the same batch.

Public exploits

PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.

Research sources

Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 11 Nov 2026, 17:48.

Original description (NVD)

A flaw was found in BusyBox. When the HTTP daemon (httpd) has pre-compressed file support enabled, authentication checks are evaluated only against the requested URL path rather than the pre-compressed file being served. A remote attacker can exploit this flaw by requesting an uncompressed file path while specifying gzip encoding, bypassing password rules configured specifically for the compressed file. This vulnerability can lead to unauthorized information disclosure of sensitive files.

NVD references (2)

Sources

The tracker combines official, freely usable data sources – updated continuously:

This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.

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