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CVE-2026-53501— Thumbor has HMAC validation bypass via multiple .replace() calls when removing URL signature

Quick assessment

Affected
thumbor thumbor
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

thumbor thumbor是thumbor组织开源的一个图像处理服务。 thumbor 7.8.0之前版本存在加密问题漏洞，该漏洞源于HMAC验证过程中使用Python的.replace()方法移除签名时，会移除所有匹配的子串，导致攻击者可在URL中多次插入相同签名来操纵最终验证URL，从而绕过验证并加载来自非预期域或路径的图像。

CVSS 8.2 · High EPSS 0.35% · P26

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 1

VendorProduct Version RangeStatus
thumbor thumbor < 7.8.0 affected
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I. Basic Information for CVE-2026-53501

Vulnerability Information
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Vulnerability Title
Thumbor has HMAC validation bypass via multiple .replace() calls when removing URL signature
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
密码学签名的验证不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
thumbor 加密问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
thumbor thumbor是thumbor组织开源的一个图像处理服务。 thumbor 7.8.0之前版本存在加密问题漏洞，该漏洞源于HMAC验证过程中使用Python的.replace()方法移除签名时，会移除所有匹配的子串，导致攻击者可在URL中多次插入相同签名来操纵最终验证URL，从而绕过验证并加载来自非预期域或路径的图像。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
thumbor thumbor < 7.8.0 -

II. Public POCs for CVE-2026-53501

# POC Description Source Link Shenlong Link
AI-Generated POC Verified env Premium
Qwen3.6-35B-A3B · 37784 chars
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Vulnerability reproduction recording (real sandbox build + trigger, exclusive)
In-depth vulnerability mechanism
Trigger conditions & impact
Full executable POC code
Exploit chain & mitigation
POC zip download
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III. Intelligence Information for CVE-2026-53501

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Patches & Fixes for CVE-2026-53501 (2)

Vendor Advisories for CVE-2026-53501 (1)

Same Patch Batch · thumbor · 2026-07-31 · 6 CVEs total

CVE-2026-53502 8.7 HIGH Thumbor has path traversal via post-validation URL decoding bypass in file_loader
CVE-2026-53500 8.2 HIGH Thumbor treats ALLOWED_SOURCES string patterns as unescaped regex, allowing hostname bypas
CVE-2026-53505 7.5 HIGH Thumbor proportion filter allows unbounded post-transform resize leading to remote DoS
CVE-2026-53503 7.5 HIGH Thumbor convolution filter allows divide-by-zero in C extension leading to remote DoS
CVE-2026-53504 7.5 HIGH Thumbor has Regex Denial of Service (ReDoS) in `convolution` filter

IV. Related Vulnerabilities

Same product: thumbor
Same vendor: thumbor
Same weakness: CWE-347

V. Comments for CVE-2026-53501

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