CVE-2025-0838: Abseil Libraries Buffer Overflow Flaw

CVE-2025-0838 Overview

A heap buffer overflow vulnerability exists in Abseil-cpp, a widely-used collection of C++ library code designed to augment the C++ standard library. The vulnerability affects the sized constructors, reserve(), and rehash() methods of absl::{flat,node}hash{set,map} containers, which fail to impose an upper bound on their size argument. This oversight allows a caller to pass an excessively large size value that causes an integer overflow when computing the size of the container's backing store, leading to out-of-bounds memory writes and potential memory corruption.

Critical Impact

Attackers with adjacent network access can exploit this integer overflow vulnerability to trigger heap buffer overflows, potentially enabling memory corruption, data integrity compromise, and code execution in applications using vulnerable Abseil hash containers.

Affected Products

• Abseil Common Libraries (all versions prior to commit 5a0e2cb5e3958dd90bb8569a2766622cb74d90c1)
• Debian Linux 11.0

Discovery Timeline

• 2025-02-21 - CVE CVE-2025-0838 published to NVD
• 2025-07-30 - Last updated in NVD database

Technical Details for CVE-2025-0838

Vulnerability Analysis

This vulnerability is classified as CWE-190 (Integer Overflow or Wraparound). The core issue lies in the memory allocation logic within Abseil's Swiss table hash container implementations. When applications call the sized constructors, reserve(), or rehash() methods with an unchecked size argument, the internal alloc_size() function calculates the total backing array size by multiplying the capacity by the slot size and adding an offset. Without proper bounds checking, exceptionally large size values can cause this multiplication to wrap around, resulting in a significantly smaller memory allocation than expected.

The vulnerability is exploitable from an adjacent network with high attack complexity. While the attack requires local privileges and active user interaction, successful exploitation can compromise both the vulnerable system and impact downstream systems. The integrity impact is particularly severe, allowing high-impact modifications to both the vulnerable component and subsequent systems.

Root Cause

The root cause is the absence of overflow protection in the alloc_size() method within absl/container/internal/raw_hash_set.h. The function performed arithmetic operations on user-controlled size values without verifying that the result would not exceed the maximum representable value for size_t. This allowed integer wraparound to occur, causing the allocated buffer to be smaller than the space subsequently used for storing hash table entries.

Attack Vector

Exploitation requires adjacent network access, meaning the attacker must be on the same network segment or have similar proximity to the target system. The attack involves providing maliciously crafted size parameters to vulnerable Abseil hash container operations. When an application accepts size hints from external sources (configuration files, network protocols, or user input) and passes them to Abseil container sizing methods, an attacker can trigger the integer overflow condition.

The resulting undersized allocation leads to out-of-bounds writes when the container attempts to populate entries, corrupting adjacent heap memory. Subsequent container access operations may also read or write beyond allocated boundaries.

  // Given the capacity of a table, computes the total size of the backing
  // array.
  size_t alloc_size(size_t slot_size) const {
+    ABSL_SWISSTABLE_ASSERT(
+        slot_size <=
+        ((std::numeric_limits<size_t>::max)() - slot_offset_) / capacity_);
    return slot_offset_ + capacity_ * slot_size;
  }
 

Source: GitHub Abseil-C++ Commit

The patch adds a bounds check assertion that validates the arithmetic operation will not overflow before computing the allocation size. This ensures that slot_offset_ + capacity_ * slot_size cannot exceed SIZE_MAX.

Detection Methods for CVE-2025-0838

Indicators of Compromise

• Unexpected application crashes with heap corruption signatures in applications using Abseil hash containers
• Memory access violations or segmentation faults during hash container operations
• Abnormal memory allocation patterns showing undersized allocations followed by large write operations
• Core dumps indicating out-of-bounds heap writes in raw_hash_set related code paths

Detection Strategies

• Monitor for AddressSanitizer (ASan) reports indicating heap-buffer-overflow in Abseil container code
• Implement runtime bounds checking on size parameters before passing to Abseil container sizing methods
• Deploy memory corruption detection tools such as Valgrind to identify out-of-bounds access patterns
• Review application logs for crashes correlating with hash container resize operations

Monitoring Recommendations

• Enable debug assertions in Abseil builds to catch overflow conditions during development and testing
• Implement input validation logging for any external size hints passed to container operations
• Configure heap corruption detection mechanisms (guard pages, canaries) in production environments
• Set up alerting for repeated crash patterns in services utilizing Abseil hash containers

How to Mitigate CVE-2025-0838

Immediate Actions Required

• Update Abseil-cpp to a version containing commit 5a0e2cb5e3958dd90bb8569a2766622cb74d90c1 or later
• Rebuild all applications and libraries that statically link against vulnerable Abseil versions
• For Debian 11.0 systems, apply the security update referenced in the Debian LTS Announcement
• Audit application code to identify instances where external input influences Abseil container sizing

Patch Information

The vulnerability has been addressed in the official Abseil commit. This patch adds proper bounds checking via ABSL_SWISSTABLE_ASSERT to validate that size calculations will not overflow before computing allocation sizes. Additionally, the patch adds the raw_logging.h header to support the assertion mechanism.

Debian Linux 11.0 users should consult the official Debian LTS security announcement for distribution-specific patching instructions.

Workarounds

• Implement input validation to reject excessively large size values before they reach Abseil container methods
• Cap size arguments to reasonable application-specific limits (e.g., SIZE_MAX / max_element_size)
• Consider using standard library containers as a temporary alternative if Abseil updates cannot be immediately deployed
• Enable runtime sanitizers (AddressSanitizer) in testing environments to catch exploitation attempts early

# Configuration example
# Rebuild your project with the patched Abseil version
git clone https://github.com/abseil/abseil-cpp.git
cd abseil-cpp
git checkout 5a0e2cb5e3958dd90bb8569a2766622cb74d90c1
mkdir build && cd build
cmake -DCMAKE_BUILD_TYPE=Release ..
make -j$(nproc)
sudo make install