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TI-2026-38576 Aliases CVE-2026-53501GHSA-mw3h-qjxj-6xg9

Thumbor has HMAC validation bypass via multiple .replace() calls when removing URL signature

Priority MEDIUM 42CWE-347Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Security bypass
Confidentiality · integrity · availability
None · High · Low
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-347.

Summary

Thumbor is an open-source photo thumbnail service by globo.com. Prior to 7.8.0, Thumbor’s HMAC validation can be bypassed due to the use of Python’s .replace() when removing the signature from the URL before validation. Since .replace() removes all occurrences of the substring, an attacker can insert the same signature multiple times in the URL and manipulate the final URL used for validation. This allows crafting URLs where the validated string differs from the actual requested resource, enabling loading images from unintended domains or paths. This issue is fixed in 7.8.0.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00352 29th percentileScored 2026-11-07
Fix Fixed thumbor (thumbor): 7.8.0thumbor (PyPI): 7.8.0

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
thumborthumborbefore 7.8.07.8.0Patch availableCNA
—thumbor (PyPI)before 7.8.07.8.0Patch availableGHSA-mw3h-qjxj-6xg9
  • thumbor Vendorthumbor Affected before 7.8.0 Fixed in 7.8.0 Patch available CNA
  • thumbor (PyPI) Vendor— Affected before 7.8.0 Fixed in 7.8.0 Patch available GHSA-mw3h-qjxj-6xg9

Remediation

  • Fix · CNA thumbor (thumbor) Fixed in 7.8.0
  • Fix · GHSA-mw3h-qjxj-6xg9 thumbor (PyPI) Fixed in 7.8.0 Advisory →

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-53501
  2. 2026-10-03 Alias added: GHSA-mw3h-qjxj-6xg9

References

Other 4

  • TI-2026-38577 Thumbor has path traversal via post-validation URL decoding bypass in file_loader CVSS 4.0HIGH 8.7
  • TI-2026-38575 Thumbor treats ALLOWED_SOURCES string patterns as unescaped regex, allowing hostname bypass via wildcard dot CVSS 3.1HIGH 8.2
  • TI-2026-38580 Thumbor proportion filter allows unbounded post-transform resize leading to remote DoS CVSS 3.1HIGH 7.5
  • TI-2026-38579 Thumbor has Regex Denial of Service (ReDoS) in `convolution` filter CVSS 3.1HIGH 7.5
  • TI-2026-38578 Thumbor convolution filter allows divide-by-zero in C extension leading to remote DoS CVSS 3.1HIGH 7.5

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences