CVE-2026-53941

Inspektor Gadget is a set of tools and framework for data collection and system inspection on Kubernetes clusters and Linux hosts using eBPF. From 0.27.0 until 0.53.1, the uprobe library resolver can allow an unprivileged container to consume excessive CPU and block other containers from starting by supplying a crafted /etc/ld.so.cache file while an uprobe-based gadget is active. The parser in pkg/uprobetracer/ldcache_parser.go trusts EntryCount enough to perform excessive iteration, computes cache1Len with overflowing uint32 arithmetic, and repeatedly calls readStringFromBytes in pkg/uprobetracer/bytes.go, where byte-by-byte immutable string concatenation produces quadratic work. While this processing occurs, pkg/container-hook holds the fanotify container-start pause, allowing a crafted cache to delay startup for roughly a minute, prevent Docker from starting other containers, and degrade monitoring. Processing caches from already-running containers can still consume CPU but does not hold the new-container startup pause, and the advisory establishes no confidentiality or integrity impact. This issue is fixed in version 0.53.1.

Inspektor Gadget is a set of tools and framework for data collection and system inspection on Kubernetes clusters and Linux hosts using eBPF. From 0.27.0 until 0.53.1, the uprobe library resolver can allow an unprivileged container to consume excessive CPU and block other containers from starting by supplying a crafted /etc/ld.so.cache file while an uprobe-based gadget is active. The parser in pkg/uprobetracer/ldcache_parser.go trusts EntryCount enough to perform excessive iteration, computes cache1Len with overflowing uint32 arithmetic, and repeatedly calls readStringFromBytes in pkg/uprobetracer/bytes.go, where byte-by-byte immutable string concatenation produces quadratic work. While this processing occurs, pkg/container-hook holds the fanotify container-start pause, allowing a crafted cache to delay startup for roughly a minute, prevent Docker from starting other containers, and degrade monitoring. Processing caches from already-running containers can still consume CPU but does not hold the new-container startup pause, and the advisory establishes no confidentiality or integrity impact. This issue is fixed in version 0.53.1.

Summary

An unprivileged container can block all other containers from starting on the same host by placing a crafted /etc/ld.so.cache file in its filesystem. When Inspektor Gadget attaches any uprobe-based gadget, it parses this file in the container startup path. A malicious cache causes ~53 seconds of CPU burn, during which Docker cannot start any other container. No special capabilities are required.

Severity

To be assessed — Availability impact, no confidentiality or integrity impact.

Affected Versions

All versions of Inspektor Gadget that support uprobe-based gadgets (trace_malloc, trace_open, trace_ssl, trace_grpc, etc.).

Description

When Inspektor Gadget attaches uprobe-based gadgets to containers, it resolves library paths by parsing the container's /etc/ld.so.cache file (pkg/uprobetracer/ldcache_parser.go). This file is fully controlled by the container.

The parser has three vulnerabilities:

1. Quadratic string building (pkg/uprobetracer/bytes.go:36-44): The readStringFromBytes function concatenates one byte at a time (res += string(data[i])), which is O(n²) in Go due to string immutability. With a 16MB cache file containing large regions without null terminators, this causes massive CPU and memory churn.

2. Insufficient entry count validation (pkg/uprobetracer/ldcache_parser.go:120): The EntryCount field is read directly from the untrusted file. While a per-entry bounds check prevents out-of-bounds access, the loop still iterates up to (fileSize - headerSize) / entrySize ≈ 700,000 times, calling readStringFromBytes on each iteration.

3. Integer overflow in format detection (pkg/uprobetracer/ldcache_parser.go:174): The cache1Len computation uses uint32 arithmetic (ldCache1Size + cache1.EntryCount*ldCache1EntrySize). With a crafted EntryCount, this overflows and produces a small value, causing the parser to misidentify the cache format.

Combined, these cause ~53 seconds of CPU burn per container attachment when a crafted 16MB /etc/ld.so.cache is present.

Impact

• Container runtime DoS: IG uses fanotify hooks (pkg/container-hook) to pause container startup until uprobe attachment completes. While IG is blocked processing the malicious cache, this pause is held, and Docker serializes container starts — meaning no other container can start on the host until IG finishes. This effectively causes a denial of service on the entire container runtime, not just on IG itself.
• Container startup delay: When any uprobe-based gadget is running (trace_malloc, trace_ssl, etc.), starting a container with a crafted ld.so.cache delays startup by ~1 minute.
• Monitoring degradation: The IG daemon is blocked processing the malicious cache, potentially missing events from other containers.
• Amplification: Multiple containers with crafted caches can be started simultaneously to amplify the effect.
• No special privileges required: Any container can include a crafted /etc/ld.so.cache in its image, mount one via a volume, or overwrite it at runtime before IG starts a uprobe gadget. In this last case, IG inspects all already-running containers when the gadget starts — this still burns CPU but does not block other containers from starting (since the fanotify pause only applies to new container starts).

Root Cause Analysis

In pkg/uprobetracer/ldcache_parser.go, the function readCacheFormat2 is called with the full file content:

for i := uint32(0); i < ldCache.EntryCount; i++ {
    entryOffset := ldEntriesOffset + i*ldCache2EntrySize
    if uint32(len(data)) <= entryOffset+ldCache2EntrySize {
        return nil  // bounds check stops iteration
    }
    // ... reads entry ...
    key := readStringFromBytes(data, keyOffset)    // O(n²) per call
    value := readStringFromBytes(data, valueOffset) // O(n²) per call
}

The per-entry bounds check correctly prevents out-of-bounds access, but:

• The loop iterates ~700K times…

Inspektor Gadget is a set of tools and framework for data collection and system inspection on Kubernetes clusters and Linux hosts using eBPF. From 0.27.0 until 0.53.1, the uprobe library resolver can allow an unprivileged container to consume excessive CPU and block other containers from starting by supplying a crafted /etc/ld.so.cache file while an uprobe-based gadget is active. The parser in pkg/uprobetracer/ldcache_parser.go trusts EntryCount enough to perform excessive iteration, computes cache1Len with overflowing uint32 arithmetic, and repeatedly calls readStringFromBytes in pkg/uprobetracer/bytes.go, where byte-by-byte immutable string concatenation produces quadratic work. While this processing occurs, pkg/container-hook holds the fanotify container-start pause, allowing a crafted cache to delay startup for roughly a minute, prevent Docker from starting other containers, and degrade monitoring. Processing caches from already-running containers can still consume CPU but does not hold the new-container startup pause, and the advisory establishes no confidentiality or integrity impact. This issue is fixed in version 0.53.1.

Inspektor Gadget is a set of tools and framework for data collection and system inspection on Kubernetes clusters and Linux hosts using eBPF. From 0.27.0 until 0.53.1, the uprobe library resolver can allow an unprivileged container to consume excessive CPU and block other containers from starting by supplying a crafted /etc/ld.so.cache file while an uprobe-based gadget is active. The parser in pkg/uprobetracer/ldcache_parser.go trusts EntryCount enough to perform excessive iteration, computes cache1Len with overflowing uint32 arithmetic, and repeatedly calls readStringFromBytes in pkg/uprobetracer/bytes.go, where byte-by-byte immutable string concatenation produces quadratic work. While this processing occurs, pkg/container-hook holds the fanotify container-start pause, allowing a crafted cache to delay startup for roughly a minute, prevent Docker from starting other containers, and degrade monitoring. Processing caches from already-running containers can still consume CPU but does not hold the new-container startup pause, and the advisory establishes no confidentiality or integrity impact. This issue is fixed in version 0.53.1.

Summary

An unprivileged container can block all other containers from starting on the same host by placing a crafted /etc/ld.so.cache file in its filesystem. When Inspektor Gadget attaches any uprobe-based gadget, it parses this file in the container startup path. A malicious cache causes ~53 seconds of CPU burn, during which Docker cannot start any other container. No special capabilities are required.

Severity

To be assessed — Availability impact, no confidentiality or integrity impact.

Affected Versions

All versions of Inspektor Gadget that support uprobe-based gadgets (trace_malloc, trace_open, trace_ssl, trace_grpc, etc.).

Description

When Inspektor Gadget attaches uprobe-based gadgets to containers, it resolves library paths by parsing the container's /etc/ld.so.cache file (pkg/uprobetracer/ldcache_parser.go). This file is fully controlled by the container.

The parser has three vulnerabilities:

1. Quadratic string building (pkg/uprobetracer/bytes.go:36-44): The readStringFromBytes function concatenates one byte at a time (res += string(data[i])), which is O(n²) in Go due to string immutability. With a 16MB cache file containing large regions without null terminators, this causes massive CPU and memory churn.

2. Insufficient entry count validation (pkg/uprobetracer/ldcache_parser.go:120): The EntryCount field is read directly from the untrusted file. While a per-entry bounds check prevents out-of-bounds access, the loop still iterates up to (fileSize - headerSize) / entrySize ≈ 700,000 times, calling readStringFromBytes on each iteration.

3. Integer overflow in format detection (pkg/uprobetracer/ldcache_parser.go:174): The cache1Len computation uses uint32 arithmetic (ldCache1Size + cache1.EntryCount*ldCache1EntrySize). With a crafted EntryCount, this overflows and produces a small value, causing the parser to misidentify the cache format.

Combined, these cause ~53 seconds of CPU burn per container attachment when a crafted 16MB /etc/ld.so.cache is present.

Impact

• Container runtime DoS: IG uses fanotify hooks (pkg/container-hook) to pause container startup until uprobe attachment completes. While IG is blocked processing the malicious cache, this pause is held, and Docker serializes container starts — meaning no other container can start on the host until IG finishes. This effectively causes a denial of service on the entire container runtime, not just on IG itself.
• Container startup delay: When any uprobe-based gadget is running (trace_malloc, trace_ssl, etc.), starting a container with a crafted ld.so.cache delays startup by ~1 minute.
• Monitoring degradation: The IG daemon is blocked processing the malicious cache, potentially missing events from other containers.
• Amplification: Multiple containers with crafted caches can be started simultaneously to amplify the effect.
• No special privileges required: Any container can include a crafted /etc/ld.so.cache in its image, mount one via a volume, or overwrite it at runtime before IG starts a uprobe gadget. In this last case, IG inspects all already-running containers when the gadget starts — this still burns CPU but does not block other containers from starting (since the fanotify pause only applies to new container starts).

Root Cause Analysis

In pkg/uprobetracer/ldcache_parser.go, the function readCacheFormat2 is called with the full file content:

for i := uint32(0); i < ldCache.EntryCount; i++ {
    entryOffset := ldEntriesOffset + i*ldCache2EntrySize
    if uint32(len(data)) <= entryOffset+ldCache2EntrySize {
        return nil  // bounds check stops iteration
    }
    // ... reads entry ...
    key := readStringFromBytes(data, keyOffset)    // O(n²) per call
    value := readStringFromBytes(data, valueOffset) // O(n²) per call
}

The per-entry bounds check correctly prevents out-of-bounds access, but:

• The loop iterates ~700K times…